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Environmental Chemistry

Class 11th Chemistry NCERT Exemplar Solution
Multiple Choice Questions I
  1. Which of the following gases is not a greenhouse gas?
  2. Photochemical smog occurs in a warm, dry and sunny climate. One of the following is not…
  3. Which of the following statements is not true about classical smog?…
  4. Biochemical Oxygen Demand (BOD) is a measure of organic material present in water. BOD…
  5. Which of the following statements is wrong?
  6. Sewage containing organic waste should not be disposed of in water bodies because it…
  7. Which of the following statements about photochemical smog is wrong?…
  8. The gaseous envelope around the earth is known as the atmosphere. The lowest layer of this…
  9. Dinitrogen and dioxygen are main constituents of air but these do not react with each…
  10. The pollutants which come directly in the air from sources are called primary pollutants.…
  11. Which of the following statements is correct?
  12. Which of the following practices will not come under green chemistry?…
Multiple Choice Questions Ii
  1. Which of the following conditions shows the polluted environment.…
  2. Phosphate containing fertilisers cause water pollution. Addition of such compounds in…
  3. The acids present in acid rain are _________.
  4. The consequences of global warming may be _________.
Short Answer
  1. Greenhouse effect leads to global warming. Which substances are responsible for the…
  2. Acid rain is known to contain some acids. Name these acids and where from they come in the…
  3. Ozone is a toxic gas and is a strong oxidizing agent even then its presence in the…
  4. Dissolved oxygen in water is very important for aquatic life. What processes are…
  5. On the basis of chemical reactions involved, explain how do chlorofluorocarbons cause…
  6. What could be the harmful effects of improper management of industrial and domestic solid…
  7. During an educational trip, a student of botany saw a beautiful lake in a village. She…
  8. What are biodegradable and non-biodegradable pollutants?
  9. What are the sources of dissolved oxygen in water?
  10. What is the importance of measuring BOD of a water body?
  11. Why does water covered with excessive algal growth become polluted?…
  12. A factory was started near a village. Suddenly villagers started feeling the presence of…
  13. Oxidation of Sulphur dioxide into Sulphur trioxide in the absence of a catalyst is a slow…
  14. From where does ozone come in the photochemical smog?
  15. How is ozone produced in stratosphere?
  16. Ozone is a gas heavier than air. Why does ozone layer not settle down near the earth?…
  17. Some time ago formation of polar stratospheric clouds was reported over Antarctica. Why…
  18. A person was using water supplied by Municipality. Due to shortage of water he started…
Matching Type
  1. Matching TypeIn the following questions more than one option of Column I and Column II may…
  2. Match the pollutant(s) in Column I with the effect(s) in Column II.…
  3. Match the activity given in Column I with the type of pollution created by it given in…
  4. Match the pollutants given in Column I with their effects given in Column II.…
Assertion And Reason
  1. Assertion (A): Greenhouse effect was observed in houses usedto grow plants and these are…
  2. Assertion (A): The pH of acid rain is less than 5.6.Reason (R): Carbon dioxide present in…
  3. Assertion (A): Photochemical smog is oxidising in nature.Reason (R): Photochemical smog…
  4. Assertion (A): Carbon dioxide is one of the important greenhouse gases.Reason (R): It is…
  5. Assertion (A): Ozone is destroyed by solar radiation in upper stratosphere.Reason (R):…
  6. Assertion (A): Excessive use of chlorinated syntheticpesticides causes soil and water…
  7. Assertion (A): If BOD level of water in a reservoir islessthan 5 ppm it is highly…
Long Answer
  1. How can you apply green chemistry for the following:(i) to control photochemical smog.(ii)…
  2. Green plants use Carbon dioxide for photosynthesis and return oxygen to the atmosphere,…
  3. Explain how does greenhouse effect cause global warming.
  4. A farmer was using pesticides on his farm. He used the produce of his farm as food for…
  5. For dry cleaning, in the place of tetrachloroethane, liquefied carbon dioxide with…

Multiple Choice Questions I
Question 1.

Which of the following gases is not a greenhouse gas?
A. CO

B. O3

C. CH4

D. H2O vapour


Answer:

Greenhouse gas is a gas that contributes to the greenhouse effect by absorbing infrared radiation.

Among the following option, O3, CH4 and H2O vapour are the greenhouse gas and CO is not because of CO absorbs low energy of infrared.


But CO can be put it in an indirect column of greenhouse gas because it increases the concentration of other greenhouse gases.


Question 2.

Photochemical smog occurs in a warm, dry and sunny climate. One of the following is not amongst the components of photochemical smog, identify it.
A. NO2

B. O3

C. SO2

D. Unsaturated hydrocarbon


Answer:

Photochemical smog is a type of smog produced when ultraviolet light from the sun reacts with nitrogen oxides in the atmosphere. It is visible as a brown haze, and is most prominent during the morning and afternoon, especially in densely populated, warm cities

The main components of photochemical smog are nitrogen oxides, Volatile Organic Compounds (VOCs), tropospheric ozone, and PAN (peroxyacetyl nitrate).


Among the following options, NO2, O3 and unsaturated hydrocarbon are components of photochemical smog where they required a warm, dry and sunny climate to get oxidized. SO2, on the other hand, has a reducing nature. Hence cannot be the component of photochemical smog.


Question 3.

Which of the following statements is not true about classical smog?
A. Its main components are produced by the action of sunlight on emissions of automobiles and factories.

B. Produced in a cold and humid climate.

C. It contains compounds of reducing nature.

D. It contains smoke, fog and sulphur dioxide.


Answer:

Classical smog is a mixture of sulfur dioxide and coal smoke with fog. It is called London smog because of an incident which was took placed in 1952 which was known as the Great Smog of London.

(ii) It is indeed produced in a cold and humid climate because the components which are present are of reducing nature. And sunlight is not required as here oxidizing is not taking place.


(iii) It contains compounds of reducing nature.


(iv) Classical smog results from large amounts of coal burning in an area and is caused by a mixture of smoke and sulfur dioxide. Hence, indeed it contains smoke, fog and sulphur dioxide.


On the other hand, (i) is not true for classical smog as it doesn’t require the action of sunlight, etc.


Question 4.

Biochemical Oxygen Demand (BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water sample to be __________.
A. rich in dissolved oxygen.

B. poor in dissolved oxygen.

C. highly polluted.

D. not suitable for aquatic life.


Answer:

BOD value less than 5 ppm indicates a water sample to be pure because BOD is a measurement of organic waste present in water. If BOD is more than 5 ppm then it indicates more organic waste, leading dissolved oxygen to be less because of usage of oxygen in the degradation of organic waste by microbes.

On the other hand, (ii),(iii),(iv) are elucidating to the polluted water, anti to what has explained above, making them wrong.


Question 5.

Which of the following statements is wrong?
A. Ozone is not responsible for the greenhouse effect.

B. Ozone can oxidize sulphur dioxide present in the atmosphere to sulphur trioxide.

C. The ozone hole is thinning of the ozone layer present in the stratosphere.

D. Ozone is produced in the upper stratosphere by the action of UV rays on oxygen


Answer:

Greenhouse gas is a gas that contributes to the greenhouse effect by absorbing infrared radiation.

Ozone, high in the stratosphere, absorbs ultraviolet light from the sun and protects the earth. It is a greenhouse gas and it is responsible for the greenhouse effect.


On the other hand, (ii),(iii),(iv) are the wrong statements.


Question 6.

Sewage containing organic waste should not be disposed of in water bodies because it causes major water pollution. Fishes in such polluted water die because of
A. Large number of mosquitoes.

B. Increase in the amount of dissolved oxygen.

C. The decrease in the amount of dissolved oxygen in the water.

D. Clogging of gills by mud.


Answer:

Due to the increase in organic waste, BOD value increases and dissolved oxygen, making fishes die due to less oxygen.

(i) It can not be a reason for fishes die in water as there is nothing to do with a large number of mosquitoes. Both can live independently.


(ii) This second statement cannot be a reason too as it is a false statement. Due to organic waste, dissolved oxygen actually decreases.


(iv) It is a false statement as mud cannot be a reason for the clogging of gills. It is sedimentary pollution that causes fish gills to be clogged.


Question 7.

Which of the following statements about photochemical smog is wrong?
A. It has a high concentration of oxidising agents.

B. It has a low concentration of the oxidising agent.

C. It can be controlled by controlling the release of NO2, hydrocarbons, ozone, etc.

D. Plantation of some plants like pinus helps in controlling photochemical smog.


Answer:

Photochemical smog is a haze in the atmosphere accompanied by high levels of ozone and nitrogen oxides, caused by the action of sunlight on pollutants.

Here components of it have a high concentration of oxidising agents. Moreover, pinus release various volatile organic gases which get reacted with components of photochemical smog and reduces the ambient concentration of ozone, NO2, hydrocarbon, etc.


Question 8.

The gaseous envelope around the earth is known as the atmosphere. The lowest layer of this is extended up to 10 km from sea level, this layer is _________.
A. Stratosphere

B. Troposphere

C. Mesosphere

D. Hydrosphere


Answer:

Troposphere is the lowest layer of the atmosphere. It extends upward to about 10km above sea level. And it is followed by another layer named stratosphere and then mesosphere. The hydrosphere includes water that is on the surface of the planet, underground, and in the air.


Question 9.

Dinitrogen and dioxygen are main constituents of air but these do not react with each other to form oxides of nitrogen because of _________.
A. the reaction is endothermic and requires a very high temperature.

B. the reaction can be initiated only in the presence of a catalyst.

C. oxides of nitrogen are unstable.

D. N2 and O2 are unreactive.


Answer:

In the environment, 78% of dinitrogen gas and 21% of dioxygen gas is present still cannot react because the reaction is endothermic and requires very high temperature. Nitrogen oxide is formed at a very high temperature.

(ii) The catalyst lowers the energy of formation. Here only in the presence of a catalyst, the reaction cannot be initiated.


(iii) Oxides of nitrogen like NO2 is resonance stabilized and some others are relatively unstable.


Question 10.

The pollutants which come directly in the air from sources are called primary pollutants. Primary pollutants are sometimes converted into secondary pollutants. Which of the following belongs to secondary air pollutants?
A. CO

B. Hydrocarbon

C. Peroxyacetyl nitrate

D. NO


Answer:

Peroxyacetyl nitrates (PANs) are produced in the atmosphere when oxidized volatile organic compounds combine with nitrogen oxide. They are secondary pollutants because they formed after the emission of primary pollutants.


Question 11.

Which of the following statements is correct?
A. The ozone hole is a hole formed in the stratosphere from which ozone oozes out.

B. The ozone hole is a hole formed in the troposphere from which ozone oozes out.

C. The ozone hole is thinning of the ozone layer of the stratosphere at some places.

D. Ozone hole means vanishing of ozone layer around the earth completely.


Answer:

(i),(ii) cannot be correct as ozone does not ooze out from the stratosphere or troposphere respectively.

(iv) cannot be correct because the ozone hole does not mean the vanishing of the ozone layer around the earth completely. The ozone hole is thinning of the ozone layer of the stratosphere at some places.


Question 12.

Which of the following practices will not come under green chemistry?
A. If possible, making use of soap made of vegetable oils instead of using synthetic detergents.

B. Using H2O2 for bleaching purposes instead of using chlorine-based bleaching agents.

C. Using a bicycle for travelling small distances instead of using petrol/ diesel-based vehicles.

D. Using plastic cans for neatly storing substances.


Answer:

Green chemistry is a way of thinking and is about utilizing the existing knowledge and principles of chemistry and other sciences to reduce the adverse impact on the environment.

As we know plastic is a non-biodegradable waste so using it, will not reduce the adverse impact on the environment.



Multiple Choice Questions Ii
Question 1.

Which of the following conditions shows the polluted environment.
A. the pH of rainwater is 5.6.

B. amount of carbon dioxide in the atmosphere is 0.03%.

C. biochemical oxygen demand 10 ppm.

D. eutrophication.


Answer:

More than BOD 5 ppm in water means the water is polluted and eutrophication itself leads to loss of biodiversity, killing fishes and various creatures living inside water. Hence iii, iv shows polluted environment.


Question 2.

Phosphate containing fertilisers cause water pollution. Addition of such compounds in water bodies causes __________.
A. enhanced growth of algae.

B. decrease in amount of dissolved oxygen in water.

C. deposition of calcium phosphate.

D. increase in fish population


Answer:

•Addition of Phosphate containing fertilisers in water bodies cause water pollution due to enhanced growth of algae.

•Due to that oxygen concentration decreases in water.


Question 3.

The acids present in acid rain are _________.
A. Peroxyacetylnitrate

B. H2CO3

C. HNO3

D. H2SO4


Answer:

Acid rain is a by-product of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere.

2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)


4NO2 (g) + O2 (g) + 2H2O (l) → 4HNO3 (aq)


so the end product is (iii, iv)


Question 4.

The consequences of global warming may be _________.
A. increase in average temperature of the earth

B. melting of Himalayan Glaciers.

C. increased biochemical oxygen demand.

D. eutrophication.


Answer:

Consequences of global warming lead to an increase in the average temperature of the earth and thus melting of Himalayan glaciers also gets into the picture.



Short Answer
Question 1.

Greenhouse effect leads to global warming. Which substances are responsible for the greenhouse effect?


Answer:

Sun radiation is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds (CFCs) and water vapour which are all greenhouse gases that are responsible for the greenhouse effect leading to global warming.



Question 2.

Acid rain is known to contain some acids. Name these acids and where from they come in the rain?


Answer:

When pH of rain water is below 5.6 then it is acid rain. Acid rain is a by-product of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere.

2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)


4NO2 (g) + O2 (g)+ 2H2O (l) → 4HNO3 (aq) . Nitric acid and sulphuric acid are acids present in acid rain.



Question 3.

Ozone is a toxic gas and is a strong oxidizing agent even then its presence in the stratosphere is very important. Explain what would happen if ozone from this region is completely removed?


Answer:

The UV radiation is harmful to any living species because it causes mutagens in our cells, skin cancers, melanoma, and many other diseases. Ozone in the stratosphere absorbs this UV radiation from the Sun and does not let pass it to the inner atmosphere. If ozone from this region is completely removed, many health issues will be encounter.



Question 4.

Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?


Answer:

Eutrophication is the process responsible for the reduction of dissolved oxygen in the water. It is a process in which nutrient-enriched water bodies support a dense plant population, which kill animal life by depriving of oxygen and result in subsequent loss of biodiversity.



Question 5.

On the basis of chemical reactions involved, explain how do chlorofluorocarbons cause thinning of ozone layer in stratosphere.


Answer:

In the stratosphere due to the action of U.V rays causes the dissociation of cloroflorocarbons to realese the free chlorine radicle as shown in the equation below:

CF2Cl2 + U V radiations → Cl + CFCl


Now this Chlorine radicle so formed is free and in the stratospheric layer reacts with the Ozone to form Chlorine monoxide and oxygen as shown in the equation below:


Cl (g) +O3 (g) → ClO (g)+O2(g)


Now further the reaction of chlorine monoxide with the nascent oxygen ie. Oxygen atom leads to the formation of oxygen and again chlorine free radical is formed as shown in the equation below:


ClO (g) + O (g) →Cl + O2


This way Chlorine radicles are being regenerated and are reacting with ozone layer. So, CFCs are considered as the source of chlorine radicles which are destroying the ozone layer of stratosphere.



Question 6.

What could be the harmful effects of improper management of industrial and domestic solid waste in a city?


Answer:

The improper disposal of waste materials is the major source or cause of environment pollution. If the domestic waste is not disposed of properly it leads to the following problems:


• Domestic waste means the household wastes which if not disposed of properly leads to chokage of sewer lines.


• Choking of sewage lines leads to the stagnation of sewage water which may become the breeding ground for the pathogenic mosquitoes.


• Imroper disposal of house hold waste which includes nonbiodegradable waste like glass, polythene in open grounds may lead to the chokage of gut of the cattle which may happen to eat the polythene along with food which may even lead to death of such organisms.


• Improper management of such domestic wastes contributes to soil pollution to a large extent.


Improper disposal or management of industrial waste is major cause of soil, water and air pollution.


Soil pollution is caused by the dumping of harmful chemicals generated by industries which penetrates in soil and get mixed with ground water.


Water pollution is caused by directly by disposing the used water waste from industries to rivers or ponds.


Air pollution is caused by the harmful smokes being generated by industries pollutes the fresh air of the atmosphere.



Question 7.

During an educational trip, a student of botany saw a beautiful lake in a village. She collected many plants from that area. She noticed that villagers were washing clothes around the lake and at some places waste material from houses was destroying its beauty.

After few years, she visited the same lake again. She was surprised to find that the lake was covered with algae, stinking smell was coming out and its water had become unusable. Can you explain the reason for this condition of the lake?


Answer:

The reason for the destroyed condition of lake was due to the disposing of the domestic waste generated in the houses of vilaggers and organic compounds like detergent in the lake Can provide nutrients for the rapid growth of algae and the aquatic plants and the decomposition of these with the help of bacteria produces foul smell. With the time the concentration of the nutrients in the lake increases. This development of plants in nutrient rich lake is due to the process called eutrophication.



Question 8.

What are biodegradable and non-biodegradable pollutants?


Answer:

Biodegradable pollutants.


Pollutants which are easily decomposed by the bacteria or other microorganisms or by various environmental factors like waste of vegetables fruits, sewage, cow dung etc are called as biodegradable pollutants.


Non biodegradable pollutants.


Pollutants which are not easily decomposed by the bacteria or any other environmental factors and remains as such in the environment and pollutes it eg polythene, DDT, mercury, aluminium etc are called as non biodegradable pollutants.



Question 9.

What are the sources of dissolved oxygen in water?


Answer:

Main sources of dissolved oxygen in water are:


• Oxygen reaches the water through the atmosphere where there is direct contact of water with atmospheric air.


• By photosynthesis through green aquatic plants in the presence of day light. In night the photosynthesis does not take place but the plants respire but the amount of oxygen is reduced.


• By mechanical aeration.



Question 10.

What is the importance of measuring BOD of a water body?


Answer:

Biochemical oxygen demand (BOD) is defined as the amount of oxygen required by the bacteria to decompose the organic.


matter present in the certain volume of sample water.


Higher the BOD of water highly polluted is the water. Lesser the BOD of water less polluted is the water.


Drinking water have BOD of the range of less than 5ppm and highly polluted water have BOD of the value of 17ppm or more.



Question 11.

Why does water covered with excessive algal growth become polluted?


Answer:

Contamination of water or any water bodies with the high amount of phosphate from the inflow of agricultural waste water polluted with fertilizers and pesticides and the disposing off the industrial waste water can contaminate the water with phosphates which leads to the rapid growth of algae in the water, turning the water and water body whole green is called Algal bloom. The decomposition of algae by the bacteria continuously produces foul smell and the algae makes water polluted and undesirable. The amount of dissolved oxygen also decreases and can lead to death of aquatic animals.



Question 12.

A factory was started near a village. Suddenly villagers started feeling the presence of irritating vapors in the village and cases of headache, chest pain, cough, dryness of throat and breathing problems increased. Villagers blamed the emissions from the chimney of the factory for such problems. Explain what could have happened. Give chemical reactions for the support of your explanation.


Answer:

The symptoms observed in the village people are same caused when there is the presence of oxides of nitrogen and sulphur in the atmosphere. These oxides are produced by the industriesthrough oxidation of fossil fuels like coal gasoline etc.


The fossil fuels containing nitrogen burns in presence of oxygen to produce a variety of oxides of nitrogen as shown in the equation below:


N2 (g) + O2 (g) → 2 NO (g)


2NO (g) + O2 (g) → 2 NO2


The fossil fuels containing sulphur also burns in air containing oxygen to produce oxides of sulphur causing various breathing problems.


S + O2 → SO2


These oxides produced by the industries comes out to atmospheric air through chimneys causing air pollution and breathing problem for living beings.



Question 13.

Oxidation of Sulphur dioxide into Sulphur trioxide in the absence of a catalyst is a slow process but this oxidation occurs easily in the atmosphere. Explain how does this happen. Give chemical reactions for the conversion of SO2 into SO3.


Answer:

Uncatalysed reaction of oxidation of sulphur dioxide to sulphur trioxide is very slow. But in the atmosphere the sulphur dioxide is easily being oxidised to sulphur trioxide because the air in the atmosphere contains particulate matter which acts as a catalyst for the oxidation reaction.


2SO2 (g) + O2 (g) → 2SO3 (g)


For eg the reaction can also be promoted by the the presence of ozone and hydrogen peroxide the oxidation of sulphur dioxide takes place as according to the given equations:


SO2 (g) + O3 (g) → SO3 (g) +O2 (g)


SO2 (g) + H2O2 (L) → H2SO4 (aq)



Question 14.

From where does ozone come in the photochemical smog?


Answer:

The composition of photochemical smog is nitrogen oxides, Volatile organic compounds (VOC), ozone, PAN i.e. peroxyacetyl nitrate.


Now the nitrogen oxide present in the smog undergoes dissociation in the presence of sunlight to NO and nascent oxygen (O) .as shown in the reaction below:


NO2 (g) → NO (g) + O (g)


The nascent oxygen is very reactive and reacts with the oxygen gas to form Ozone gas along with the inert gas which promotes their reaction. After the reaction inert gas is obtained as it is without reacting with any of the species. As depicted by the reaction below:


O (g) + O2 (g) + M → O2 (g) + M


Where M = inert gas.



Question 15.

How is ozone produced in stratosphere?


Answer:

Ozone layer is formed in the stratosphere by the action of U. V radiations on the atmospheric oxygen. UV radiations causes the splitting or dissociation of molecular oxygen to two oxygen atoms as shown below in the reaction:


O 2 (g) → O (g) + O (g)


Now the oxygen atom combines with other molecular oxygen to form Ozone as shown in the equation below:


O (g) + O2 (g) → O3 (g)



Question 16.

Ozone is a gas heavier than air. Why does ozone layer not settle down near the earth?


Answer:

Ozone layer is heavier than oxygen and is thermodynamically unstable and there is a dynamic equilibrium in the reaction between formation and dissociation of the ozone as shown:


O2 (g) → O (g) + O (g)


O (g) + O2 (g) → O3 (g)


(reaction is in dynamic equilibrium)


Since it’s thermodynamically unstable so it does not settle down near the earth.



Question 17.

Some time ago formation of polar stratospheric clouds was reported over Antarctica. Why were these formed? What happens when such clouds break up by warmth of sunlight?


Answer:

Scientists working in the Antarctica reported the depletion of ozone layer called ozone hole over the south pole of the Antarctica. This time the depletion was reported due to unique set of conditions. In the summer season the nitrogen dioxide and methane reacted with the chlorine monoxide and chlorine radicle respectively forming chlorine sinks thereby preventing the depletion of ozone.


ClO + NO2 (g) → ClONO2


Cl (g) + CH4→ CH3(g) + HCl (g)


ClONO2 (g) +H2O → HOCl (g) + HNO3


ClONO2 (g) + HCl → Cl2 (g) + HNO3 (g)


Wherease in winters the formation of polar stratospheric clouds was observed over the entire Antarctic region. These clouds were reported to act as a surface over where the chlorine nitrate formed got hydrolysed to form hypochlorous acid. The acid thus formed reacted with hydrogen chloride to form molecular chlorine.


HOCl (g) → OH (g) Cl (g)


Cl + Cl Gives molecular chlorine


When the sunlight returned back in the spring it led to breaking up of clouds and HOCl and molecular chlorine gets photolysed by sunlight to form chlorine radicles as shown below:


Cl2 (g) → 2 Cl


These chlorine radicles further caused the ozone depletion.



Question 18.

A person was using water supplied by Municipality. Due to shortage of water he started using underground water. He felt laxative effect. What could be the cause?


Answer:

Laxative effect is the effect caused by laxative substances that loosen stools and increases bowel movement. High doses of laxatives may even cause diarrhea.


Study on it reported that the presence of excessive sulphate (greater than 500 ppm) in the drinkingwater is the major cause of it. When sulphate is present in moderate amounts it is harmless.




Matching Type
Question 1.

Matching Type

In the following questions more than one option of Column I and Column II may match.

Match the terms given in Column I with the compounds given in Column II.



Answer:

Match it




Question 2.

Match the pollutant(s) in Column I with the effect(s) in Column II.



Answer:

(i) Oxides of sulphur - (d) Respiratory diseases

Explanation:Oxides of sulphur are produced when sulphur-containing fossil fuel is burnt. The most poisonous gas is sulphur dioxide which in low concentrations can cause respiratory diseases like asthma, bronchitis, emphysema in human beings.


(ii) Nitrogen dioxide - (e) Red haze in traffic and congested areas


Explanation:The irritant red haze in the traffic and congested places is due to oxides of nitrogen. Nitric oxide reacts with oxygen instantly to give nitrogen dioxide and the rate of nitrogen dioxide is faster when nitric oxide reacts with ozone in the stratosphere.


(iii) Carbon dioxide - (a) Global warming


Explanation:Carbon dioxide is released into the atmosphere by numerous ways which include respiration by animals and plants, fossil fuels burning for retrieval of energy and by decomposition of limestone during the manufacturing of cement. Deforestation and burning of fossil fuel increase the Carbon dioxide level and disturb the balance in the atmosphere. Carbon dioxide is mainly responsible for causing and promoting global warming.


(iv)Nitrate in drinking water -(c) ‘Blue baby’ syndrome


Explanation:Purified or clean drinking water is generally used for various purposes which include – drinking, cooking or cleaning etc. so as to avoid the occurrence of any kind of diseases. According to the International Standards, the maximum limit of nitrate that can be present in drinking water is 50ppm. On the other hand, excess nitrate in drinking water can lead to cause methemoglobinemia or commonly called as ‘blue baby syndrome’.


(v) Lead - (b) Damage to kidney


Explanation:Hygiene is of prime importance. To stay fit and fine we must drink and eat hygienic, covered, clean and nutritious food/water. Sometimes, if we consume contaminated water/food we acquire various diseases.According to the International Standards, the upper limit of concentration of lead in drinking water is to be 50 ppb. Otherwise, Pbcan cause variousproblems kidney, liver, reproductive system etc.



Question 3.

Match the activity given in Column I with the type of pollution created by it given in Column II.



Answer:

(i) Releasing gases to the atmosphere after burning waste material containing sulphur - (e) Classical smog,acidrain, water pollutioncleaning computer parts induce problems, damage tobuildings, corrosion of metals.

Explanation: Releasing gases to the atmosphere produced by automobiles and factories may cause classical smog, acid rain and induce problems, damage to buildings and corrosion of metals. Classical smog is one of the pollutants which occurs in cool and humid climate. It is of reducing in nature.


(ii) Using carbamates as pesticides - (d) May cause nerve diseases in human.


Explanation:Carbamates and organo-phosphates are bio-degradable products and less persistent. These chemicals are severe nerve toxins and hence more harmful to humans and could lead to death.


(iii) Using synthetic detergents for layer washing clothes - (a) Water pollution


Explanation:Use of synthetic detergents for washing clothes may lead to water pollution and depletion of fresh water.


(iv)Releasing gases produced byautomobiles and factoriesin the atmosphere - (b) Photochemical smog, damageto plant life, corrosion to building material, induce breathing problems, water pollution


Explanation: Photochemical smog occurs in warm, dry sunny climate. The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. It has high concentration of oxidising agents and damage plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surfaces. It is of oxidising in nature and occurs in dry and sunny climate.


(v) Using chlorofluorocarbon compounds - (c) Damaging ozone layer


Explanation:The main reason for ozone layer depletion is due to the release of Chlorofluorocarbons (CFCs), also commonly referred to as freons. These compounds are non-reactive, non-flammable, non-toxic organic molecules and therefore, used in refrigerators, air conditioners and for cleaning computer parts.



Question 4.

Match the pollutants given in Column I with their effects given in Column II.



Answer:

(i) Phosphate fertilisers in water - (d) Eutrophication

Explanation:Phosphate fertilisers in water can enhance algal growth which could cover the water surface and reduces the oxygen concentration in the water. This leads to anaerobic conditions, commonly with accumulation of decay and animal death. This algal bloom inhibits the growth of other living organisms in the water body. This process is called eutrophication.


(ii) Methane in air - (c) Global warming


Explanation:Methane is produced naturally when vegetation is burnt, digested or rotted in the absence of oxygen. Large amounts of methane are released from paddy fields, coal mines and by fossil fuels. It contributes to global warming.


(iii) Synthetic detergents in water - (a) BOD level of water increases


Explanation:Synthetic detergents in water could result in reduction of dissolved oxygen and therefore, increase in BOD level of water. The amount of BOD in the water is a measure of amount of organic material in the water.


(iv) Nitrogen oxides in air – (b) Acid Rain


Explanation:Acid rain is a by-product of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere. Acid rain is harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth. It causes respiratory ailments in human beings and animals. When acid rain falls and flows as ground water to reach rivers, lakes etc. it affects plants and animal life in aquatic ecosystem.




Assertion And Reason
Question 1.

Assertion (A): Greenhouse effect was observed in houses usedto grow plants and these are made of green glass.

Reason (R): Greenhouse name has been given because glass houses are made of green glass.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.


Answer:

(i) Both A and R are correct and R is the correct explanation of A.

Explanation:Sun is the major source of light energy and it is required by all the organism for sustaining their lives. The Sun radiates its rays which enter into the Earth’s atmosphere but due to the presence of ozone, it doesn’t able to escape. This results in the increase of the temperature inside the Earth. This is known as Greenhouse Effect. In the greenhouses the factors which regulate or drive the normal physiological processes/functioning of the plants get accelerated. Temperature (controlled by heaters or fans etc), humidity, soil aeration, irrigation, fertility levels and controlled light amounts are required for the optimum growth of plants. Therefore, plants are able to grow properly and yield more amount of biomass due to the availability of these safe and protected conditions.


The greenhouses are generally transparent buildings or big rooms which are made up of glass (PMMA/ acrylic glass)or green glassor plastic (polyethylene film) or polycarbonate material multiwall sheets which are used to trap the radiations coming from the Sun. Green glass is composed of chrome oxide (different concentrations give variations in green color). Thus, to give a typical green color, they are composed of green glass.



Question 2.

Assertion (A): The pH of acid rain is less than 5.6.

Reason (R): Carbon dioxide present in the atmosphere dissolves in rain water and forms carbonic acid.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanationof A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.


Answer:

(ii) Both A and R are correct but R is not the correct explanationof A.

Explanation:Acid rain is the rain which has been acidified by the chemicals present in the atmosphere. Due to the presence of pollutants or chemicals released from the industry (industrial smoke) or vehicular exhaust like sulphur oxides and nitrogen oxides, they react with the water vapours or water droplets andform acids of respective non-metals which in turn results in thelowering of the pH of the rain. Sometimes, carbon dioxide present in the atmosphere can also lead to lowering of pH of rain, but it isnot the sole factor responsible for lowering the pH of rain to less than 5.6.



Question 3.

Assertion (A): Photochemical smog is oxidising in nature.

Reason (R): Photochemical smog contains and , which are formed during the sequence of reactions.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation ofA.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.


Answer:

(i) Both A and R are correct and R is the correct explanation of A.

Explanation: Photochemical smog is one of the types of pollution which generally results from the reaction of atmospheric chemicals and sunlight. The primary Photochemical smog component is the ozone along with this it also contains , acrolein, PAN (Peroxy Acetyl Nitrate) and volatile organic compounds like formaldehyde.


The formation of photochemical smog involves multiple reversible oxidation/reductions steps of nitrogen oxides, methane and sulphur oxides.








Now, both nitrogen dioxide and ozone acts as oxidising agents and react with unburnt hydrocarbons and produce other components of photochemical smog – PAN, formaldehyde and acrolein.



Question 4.

Assertion (A): Carbon dioxide is one of the important greenhouse gases.

Reason (R): It is largely produced by respiratory function of

animals and plants.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct


Answer:

(i) Both A and R are correct and R is the correct explanation of A.

Explanation:Carbon dioxide is one of the main components and important greenhouses gases. Gases like methane, carbon dioxide and nitrous oxide absorb the UV radiations and prevent them from escaping from the Earth’s atmosphere, thus leading in the increaseof the temperature of the Earth’s surface which is essential for the sustenance of life. All living organism exhale carbon dioxide during the respiration process which in turn leads to the accumulation of in the atmosphere. On the other hand, increasing concentration of carbon dioxide leads to global warming as well. Therefore, the proportion of in the atmosphere should be maintained.



Question 5.

Assertion (A): Ozone is destroyed by solar radiation in upper stratosphere.

Reason (R): Thinning of the ozone layer allows excessive UV radiations to reach the surface of earth.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct


Answer:

(i) Both A and R are correct and R is correct explanation of A.

Explanation: Ozone formation takes place in the stratosphere when dioxygen reacts with free Oxygen in the presence of intense UVradiations. This ozone layer protects the Earth from the harmful radiations coming from the Sun, otherwise which cause several severe medical problems like melanoma (skin cancers) inhumans. At the same time, ozone is unstable thermodynamically,therefore, as soon as it is formed it gets decomposed tomolecular oxygen in the stratosphere. Although, this process of decomposition is being accelerated due to the usage of various anthropogenic activities or release of CFCs/freons. These chemicals are used in refrigerators, ACs etc and are non-reactive, non-toxic and non-flammable to humans but still due to the ability to produce Cl radicals continuously upon reacting with UV in the stratosphere, they contribute in the depletion or thinning ofthe ozone layers.




This reaction takes place continuously thereby resulting in destroying or scavenging ozone molecules. Thus, leading to thinning of ozone layer.



Question 6.

Assertion (A): Excessive use of chlorinated syntheticpesticides causes soil and water pollution.

Reason (R): Such pesticides are non-biodegradable.

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.


Answer:

(i) Both A and R are correct and R is the correct explanation of A.

Explanation: Excessive use of chlorinated synthetic pesticides causes soil and water pollution. This is due to the fact that fertilizers slowly get accumulated in the water bodies and start hindering with others too. This in turn cause several problems as they start migrating from one place to other water bodies with the help of rain. Also, pesticides are chemicals which can not be decomposed or degraded using the microorganisms. Therefore, they are non-biodegradable.



Question 7.

Assertion (A): If BOD level of water in a reservoir islessthan 5 ppm it is highly polluted.

Reason (R): High biological oxygen demand means low activity ofbacteria in water

(i) Both A and R are correct and R is the correct explanation of A.

(ii) Both A and R are correct but R is not the correct explanation of A.

(iii) Both A and R are not correct.

(iv) A is not correct but R is correct.


Answer:

(iii) Both A and R are not correct.

Explanation:BOD value is more than 17 ppm for the more polluted water bodies whereas it is less than 5 ppm for the clean water bodies. Biological Oxygen Demand is defined as the amount of oxygen required by the bacteria to break down the organic matter into simpler compounds. Further, the BOD value is directly related with the amount of organic matter present in the water sample which is available for the bacteria to break upon. Therefore, high biological oxygen demand value means high activity of bacteria in water.




Long Answer
Question 1.

How can you apply green chemistry for the following:

(i) to control photochemical smog.

(ii) to avoid use of halogenated solvents in drycleaning and that of chlorine in bleaching.

(iii) to reduce use of synthetic detergents.

(iv)to reduce the consumption of petrol and diesel.


Answer:

(i) The primary precursors of photochemical smog can be controlled which consists ofcompounds as Nitrogen dioxide and hydrocarbons, the secondary precursors such as ozone and PAN, the photochemical smog will automatically be reduced. Usually, catalytic converters are used in automobiles, which prevent the release of nitrogen oxide and hydrocarbons to the atmosphere. Certain plants e.g., Pinussp., Juniparussp., Quercussp., Pyrussp. and Vitissp.can metabolise nitrogen oxide and therefore, their plantation could help in this matter.

(ii) Tetra Chloroethene is now being replaced by a process, where liquefied Carbondioxide, with a suitable detergent, is used. Replacement of halogenated solvent by liquid will result in less harm to groundwater. These days hydrogen peroxide () is used for the purpose of bleaching clothes in the process of laundry, which gives better results and makes use of a lesser amount of water. Chlorine gas was used earlier for bleaching paper. These days, hydrogen peroxidewith a suitable catalyst, which promotes the bleaching action of hydrogen peroxide, is used.


(iii) Synthetic detergents are salts of Na having long chains of Benzene sulphonic acids or salts of Na having long chains of alkyl hydrogen sulphates. But unlike, other pollutants, detergents are not biodegradable as they are not acted upon by microorganisms. Due to the presence of Mg or Ca salts they are not easily degraded and they form bubbles in water where oxygen and sunlight gets tapped and they hinder the normal growth of the planktonic species growing in the water. Thus, the use of synthetic detergents should be reused.


(iv) The consumption of petrol and diesel should be reduced being fossil fuels, they release compounds containing sulphur (mainly sulphur dioxides) which get released in the atmosphere and comes on the ground in the form of acid rain by forming respective acids.





Therefore, they should be replaced by bio-diesel and bio-petrol so that environmental pollution can be controlled. These are made using green chemistry (by using plant-based materials) and eco-friendly.



Question 2.

Green plants use Carbon dioxide for photosynthesis and return oxygen to the atmosphere, even then Carbon dioxide is considered to be responsible for greenhouse effect. Explain why?


Answer:

Carbon dioxide is released into the atmosphere by various processes like respiration and burning of fossil fuels for energy, etc.

This gas is also emitted during volcanic eruptions. Carbon dioxide gas is normally found till troposphere. As the consumption of fossil fuels increases, a large amount of carbon dioxide gets released into the atmosphere. Excess of in the air is removed by green plants and this maintains an appropriate level of in the atmosphere. Green plants require for photosynthesis and they, in turn, emit oxygen, thus maintaining the delicate balance deforestation and burning of fossil fuel increases the level and disturb the balance in the atmosphere.


The increased amount of in the air is responsible for global warming. About75% of the solar energy reaching the earth is absorbed by the earth’s surface, which thereby increases the temperature. The rest of the heat radiates or reflects back in to the atmosphere. Some of the heat is trapped by gases such as , Methane, chlorofluorocarbon compounds (CFCs) and water vapour in the atmosphere.


Thus, they add to the heating of the atmosphere. Carbon dioxide molecules trap heat as they are transparent to sunlight but not to the heat radiation. If the amount of carbon dioxide crosses the delicate proportion of 0.03%, the natural greenhouse balance may get disturbed. Carbon dioxide is the major component which contributes to the global warming.



Question 3.

Explain how does greenhouse effect cause global warming.


Answer:

The glass in a greenhouse holds the sun’s warmth inside same as the atmosphere traps the sun’s heat near the earth’s surface and keeps it warm. This is called natural greenhouse effect because it maintains the temperature and makes the earth perfect for life.

In a greenhouse, solar radiations pass through the transparent glass and heat up the soil and the plants. The warm soil and plants emit infrared radiations. Since glass is opaque to infrared radiations (thermal region), it partly reflects and partly absorbs these radiations. This mechanism keeps the energy of the sun trapped in the greenhouse. Similarly, carbon dioxide molecules also trap heat as they are transparent to sunlight but not to the heat radiation. Carbon dioxide is the major contributor to global warming.



Question 4.

A farmer was using pesticides on his farm. He used the produce of his farm as food for rearing fishes. He was told that fishes werenot fit for human consumption because large amount of pesticidehad accumulated in the tissues of fishes. Explain how did this happen?


Answer:

The fishes were not fit for human consumption because large amount of pesticides had accumulated in the tissues of fishes as a result of biomagnification.Biomagnification is the process in which the pesticides get slowly accumulated in the fishes or other marine animals thereby results in the decline of other species which feed on them.



Question 5.

For dry cleaning, in the place of tetrachloroethane, liquefied carbon dioxide with suitable detergent is an alternative solvent.What type of harm to the environment will be prevented bystopping use of tetrachloroethane? Will use of liquefied carbon dioxide with detergent be completely safe from the point of view of pollution? Explain.


Answer:

Tetrachloroethylene is widely used for dry-cleaning fabrics and metal degreasing operations. Acute or short term high-level inhalation exposure of humans to tetrachloroethylene effects include irritation of the upper respiratory tract and eyes, kidney dysfunction, and neurological effects such as reversible mood and behavioral changes, impairment of coordination, dizziness, headache, sleepiness, and unconsciousness.

While the primary effects of chronic (long term) inhalation exposure involve neurological, including impaired cognitive and motor neurobehavioral performance. Tetrachloroethylene exposure may also cause adverse effects in the kidney, liver, immune system, and on development and reproduction.


Use of liquefied Carbon dioxide along with detergent will not be completely safe because most of the detergents are non-biodegradable and they cause water pollution. Moreover, liquefied
carbon dioxidewill ultimately enter into the atmosphere and contribute to the greenhouse effect. These days hydrogen peroxide is used for bleaching clothes in laundries for better quality and saves water.