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Chapter 8

Atmospheric Pollution

Class 9 - Dalal Simplified ICSE Chemistry Solutions


Questions

Question 1(2007)

Name any two natural sources of atmospheric pollution.

Answer

Two natural sources of atmospheric pollution are:

  1. Disintegration of rocks and soil.
  2. Decay of plants and animals, volcanic eruptions.

Question 2(2007)

Name any two gases which are responsible for the formation of acid rain.

Answer

  1. Oxides of sulphur SO2
  2. Oxides of nitrogen NO2

Question 3(2007)

Explain the term 'global warming'.

Answer

The warming up of the earth's surface, due to concentration or blanketing effect of the green house gases (Green house effect) results in the rise of atmospheric temperatures. This is not confined to one region but has a global impact and is termed as global warming.

Question 1(2008)

State two effects of ozone depletion.

Answer

  1. Harmful ultra-violet rays will reach the earth and cause damage.
  2. Humans, animals and plants will be adversely affected by the harmful effects of ultra violet radiations.

Question 1(2009)

What is meant by the term 'acid rain'. Give any two impacts of acid rain.

Answer

The term 'acid rain' refers to the various ways in which the acids formed in the atmosphere - condense and fall on the earth resulting in acid rain.

Impacts of acid rain :

  1. Nutrient leaching — The hydrogen ions which are added to the soil when acid rain falls on the earth interact chemically with existing soil minerals.
    H2SO4 ⇌ 2H1+ + SO42-
    Minerals like potassium and calcium interact with the H1+ ions and are displaced from the soil, thus the soil is deprived of nutrients.
  2. Affects marine organisms — Toxic metals like mercury, lead, zinc present in the soil, get leached by acid rain thus toxicity enters rivers and streams and destroys aquatic plants and animals.

Question 2(2009)

State two ways by which global warming can be reduced.

Answer

Global warming can be reduced by reducing the emission of green house gases by :

  1. Using different fuels which release less green house gases:
    1. Liquefied Petroleum Gas [L.P.G.] — contains mostly propane [C3H8]
    2. Liquefied Natural Gas [L.N.G.] — contains mostly methane [CH4]
    3. Compressed Natural Gas [C.N.G.] — similar to L.P.G. but is not liquefied.
  2. Using renewable energy resources like :
    1. Solar energy [from sun's stored energy]
    2. Wind energy [from windmills]
    3. Hydropower energy [from high dams]

Question 3(2009)

State an advantage of using solar energy.

Answer

Solar energy is a renewable source of energy that does not cause pollution and helps in reducing global warming as it does not emit greenhouse gases.

Question 1(2010)

Explain the methods of preventing acid rain.

Answer

Method of preventing acid rain are:

  1. Using alternate energy sources — alternatives to burning of fossil fuels such as compressed natural gas [C.N.G.] or use of cleaner energy sources such as hydro power or wind energy causes almost no pollution.
  2. Usage of technical devices — such as catalytic convertors, which can reduce nitrogen oxide emissions from automobiles [usage of electrostatic precipitators in industries].

Question 2(2010)

State an advantage of CNG [compressed natural gas].

Answer

CNG is an alternative to petrol and diesel since it causes minimum pollution. It does not contain lead and lowers maintenance cost as compared to vehicles with other forms of fuels.

Question 3(2010)

State how CFCs break ozone in the stratosphere.

Answer

The breakdown of ozone by CFCs in the stratosphere is brought about in the following way:

  1. Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.
  2. By products of the breakdown of CFCs results in increase in levels of free radicals of atomic chlorine [Cl].
  3. The free radicals initiate and catalyse a chain reaction by reacting with ozone to form chlorine monoxide (ClO) and oxygen (O2). These reactions are capable of breakdown of over 1,00,000 ozone molecules resulting in ozone depletion.
State how CFCs break ozone in the stratosphere. Atmospheric Pollution, Simplified Chemistry Dalal Solutions ICSE Class 9.

Question 4(2010)

Describe the methods of saving the ozone layer.

Answer

  1. Use of products that contain CFC's to be replaced by alternative products.
  2. Substitutes for CFC's have been initiated by scientists and use of HCFC [hydrochlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.
  3. International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

Additional Questions

Question 1

State what is meant by the term 'atmospheric pollution'. Name four gaseous atmospheric pollutants.

Answer

Atmospheric pollution means conditions of air made unclean due to introduction of foreign elements from (i) Natural sources (ii) Man made sources to the air so as to cause adverse effects on living organisms on earth.

Four gaseous pollutants are:

  1. Oxides of sulphur [SO2],
  2. Oxides of nitrogen [NO],
  3. Oxides of carbon [CO2],
  4. Hydrogen sulphide [H2S]

Question 2

Explain the term 'acid rain'. State the two forms of deposition of acid rain with suitable examples of each form of deposition.

Answer

The term 'acid rain' refers to the various ways in which the acids formed in the atmosphere condense and fall on the earth.

The two forms of depositions of acid rain are:

  1. Wet deposits - rain, snow, fog, dew
  2. Dry deposits - particles [containing sulphates and nitrates]

Question 3

State the natural and man-made sources of the two pollutants responsible for acid rain.

Answer

  1. Natural sources — bacterial decomposition, forest fires, volcanic eruptions
  2. Man made sources — power, industrial and smelting plants and automobile exhausts.

Question 4

Burning of fossil fuels is an important source of the pollutant – 'oxides of sulphur' responsible for acid rain. State what are 'fossil fuels'. Name the principal fossil fuels. State why sulphur dioxide is emitted on burning a fossil fuel. Give a balanced equation for the same.

Answer

Fuels that are derived from organic remains of plants and animals are called fossil fuels.
Principal fossil fuels — coal, petroleum [oil], natural gas.
Sulphur impurities are present in fossil fuels which produce sulphur dioxide when the fossil fuel is burnt. Balanced chemical equation for the same is given below:
S + O2 ⟶ SO2

Question 5

During metallurgy – smelting plants produce sulphur dioxide, when metallic sulphides are roasted in air. Give a balanced equation for the same.

Answer

Balanced equation representing the emission of sulphur dioxide when metallic sulphides are roasted in air is given below:

2ZnS + 3O2 ⟶ 2ZnO + 2SO2

Question 6

State why high temperatures in internal combustion engines release pollutant – oxides of nitrogen.

Answer

In internal combustion engines, combustion of fossil fuel occurs with an oxidiser (air). The air drawn from the atmosphere contains about 80% nitrogen. The nitrogen combines with oxygen at high temperature producing oxides of nitrogen.

N2 + O2 ⟶ 2NO [at high temp.]

Thus, exhaust gases of all internal combustion engines release oxides of nitrogen.

Question 7

State why natural rain water produced in an unpolluted atmosphere is slightly acidic. Give a balanced equation of the same.

Answer

Natural rain water produced in an unpolluted atmosphere is slightly acidic as CO2 present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H2CO3].

H2O + CO2 ⟶ H2CO3 [carbonic acid]

Question 8

Give balanced equations for the formation of sulphuric acid in acid rain, when a fossil fuel is burnt in an electric power station.

Answer

  1. When a fossil fuel is burnt in an electric power station sulphur dioxide is formed:
    S + O2 ⟶ SO2
  2. Sulphur dioxide reacts with water vapour to form sulphurous acid
    H2O + SO2 ⟶ H2SO3 [aq.]
  3. Sulphur dioxide can also be oxidized to sulphur trioxide [SO3]
    2SO2 + O2 ⟶ 2SO3
    [The reaction is catalyzed by dust particles and water droplets].
  4. Sulphur trioxide reacts with water vapour in air forming sulphuric acid
    H2O + SO3 ⟶ H2SO4 [aq.]

Thus, the acidity of rain is due to reaction of oxides of sulphur with water vapour forming dilute acids.

Question 9

Starting from nitrogen in air, enlist the reactions with the help of balanced equations, which result in the conversion of nitrogen in an internal combustion engine, to the acids formed which are responsible for acid rain.

Answer

  1. Nitrogen combines with oxygen at high temperatures to give nitric oxide
    N2 + O2 → 2NO
  2. Nitric oxide [NO] is oxidized to nitrogen dioxide [NO2]
    2NO + O2 ⟶ 2NO2
  3. Nitrogen dioxide [NO2] reacts with water vapour to form nitrous acid [HNO2] and nitric acid [HNO3]
    H2O + 2NO2 ⟶ HNO2 + HNO3
    [The nitrogen dioxide may also dissolve in atmospheric moisture in the presence of oxygen of the air forming nitric acid in the free state].
    [2H2O + 4NO2 + O2 ⟶ 4HNO3]

Thus the acidity in the rain is due to reaction of oxides of nitrogen with water vapour forming dilute acids.

Question 10

Explain the basic function of a catalytic converter in an internal combustion engine.

Answer

The basic function of a catalytic converter in internal combustion engine is to help reduce pollution.

The reduction catalyst [Pt/Pd] in a converter separates the nitrogen atom from NO and NO2 molecules freeing oxygen in the form of O2 molecule.

2NO ⟶ N2 + O2
2NO2 ⟶ N2 + 2O2

Thus, the oxides of nitrogen which are pollutants are converted to free nitrogen.

Question 11

State why acid rain causes 'nutrient leaching' when it falls on the earth.

Answer

The hydrogen ions which are added to the soil - when acid rain falls on the earth - interact chemically with existing soil minerals.

H2SO4 ⇌ 2H1+ + SO42-

Minerals like potassium and calcium interact with the H1+ ions and are displaced from the soil, thus the soil is deprived of nutrients causing nutrient leaching.

Question 12

Give reasons why acid rain affects marine organisms.

Answer

Toxic metals like - mercury, lead, zinc present in the soil, get leached by acid rain thus toxicity enters rivers and streams and destroys aquatic plants and animals.

Question 13

State the impact of acid rain on the environment, other than soil chemistry and water bodies.

Answer

Acid rain affects :

  1. Plants in numerous ways — affects transpiration, decolourises leaf pigments, retards growth of crops and reduces rate of photosynthesis.
  2. Humans — Acid rain gets absorbed by plants, animals and directly or indirectly toxicity enters food chain affecting humans.
  3. Material Damage — Corrodes metallic surfaces, disintegrates paper and leather, weakens building material such as statues, sculptures, marbles, limestone [CaCO3] etc.
    CaCO3 + H2SO4 ⟶ CaSO4 + H2O + CO2

Question 14

Enumerate the ways by which acid rain can be controlled to prevent it's adverse effects on the environment.

Answer

Ways to control acid rain:

  1. Using alternate energy sources - alternatives to burning of fossil fuels such as compressed natural gas [C.N.G.] or use of cleaner energy sources such as hydro power or wind energy causes almost no pollution.
  2. Usage of technical devices - such as catalytic convertors, which can reduce nitrogen oxide emissions from automobiles [usage of electrostatic precipitators in industries].

Question 15

State what are 'green house gases' and name the major green house gases.

Answer

Green house gases are those gases that contribute effectively in retaining heat in the atmosphere.
Major green house gases are carbon dioxide, methane, water vapours, oxides of nitrogen and chlorofluorocarbons.

Question 16

State what is meant by the term – 'green house effect' and state it's consequence.

Answer

Green house effect is the warming up of the earth's surface, due to concentration or blanketing effect of the green house gases.

The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.

Question 17

Explain how global warming takes place in the presence of green house gases. Give a reason why the surface temperature of earth is maintained in absence of green house gases.

Answer

The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as global warming.

In absence of green house gases the surface temperature on earth is maintained since -

  1. The solar radiations emitted as heat radiations, passes through the clear atmosphere.
  2. It reaches the earth's surface where it is absorbed and retained.
  3. Some of the absorbed heat radiations is reflected back into the atmosphere. [radiations from the earth takes place in two ways - reflected solar radiation and emitted thermal infra red radiations]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth.

Question 18

Give balanced equations for formation of carbon dioxide – a major green house gas, during combustion of fossil fuels.

Answer

Balanced equations for formation of carbon dioxide during combustion of fossil fuels are given below:

  1. Burning of Coal
    C + O2 ⟶ CO2 + Δ
  2. Burning of Natural gas
    CH4 + 2O2 ⟶ CO2 + 2H2O + Δ

Question 19

State two natural and two man-made sources of the green house gas – methane.

Answer

Two natural sources of Methane are:

  1. Bacterial decay of vegetable matter releases marsh gas which is mainly methane.
  2. Natural gas associated with petroleum contains about 75% of methane.

Two man-made sources of Methane are:

  1. Natural wet lands and rice paddies
  2. Gas drilling, Coal mining, biomass burning

Question 20

'Oxides of nitrogen namely nitrous oxide, are released into the atmosphere from varied sources'. Explain the statement with relevant sources.

Answer

Oxides of nitrogen (namely nitrous oxide), are released into the atmosphere from various natural and man-made sources. The natural sources are:

  1. Anaerobic respiration — Activities of micro organisms in soil release nitrogen, nitric oxide and nitrous oxide.
  2. The lightning discharge in the atmosphere creates high temperatures causing Nitrogen (N2) and Oxygen (O2) to combine forming Oxides of Nitrogen.

The man-made sources are:

  1. Use of nitrogenous fertilizers for agricultural activities release oxides of nitrogen.
  2. Automobile exhausts.
  3. Burning of biomass.

Question 21

State the impact of green house gases on geographic, climatic and agricultural conditions.

Answer

Impact of green house gases on:

  1. Geographic conditions — Global warming increases melting of ice-caps which results in rising of sea levels causing coastal floating and erosion.
  2. Climatic conditions — Tropical regions experience more rainfall. Northern latitudes experience shorter and wetter winters.
  3. Agricultural conditions — Affects due to climatic changes:
    1. the life cycle of trees and survival and reproduction of plants.
    2. the soil fertility and amount of soil water retained in the soil.

Question 22

Give the options for reducing green house gases by use of fuels better than fossil fuels.

Answer

The following fuels can be used which are better than fossil fuels as they release less green house gases:

  1. Liquefied Petroleum Gas [L.P.G.] - contains mostly propane [C3H8]
  2. Liquefied Natural Gas [L.N.G.] - contains mostly methane [CH4]
  3. Compressed Natural Gas [C.N.G.] - similar to L.P.G. but is not liquefied.

Question 23

State three renewable energy sources which cause less or no pollution.

Answer

Renewable sources of energy are:

  1. Solar energy [from sun's stored energy]
  2. Wind energy [from windmills]
  3. Hydropower energy [from high dams]

Question 24

Explain how promoting 'afforestation' and checking 'deforestation' reduces the release of green house gases.

Answer

Promoting afforestation means to induce more growth of plantation and forests. This helps to absorb green house gas - carbon dioxide during photosynthesis.

6CO2+12H2OChlorophyllSunlightC6H12O6+6H2O+6O26\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} \text{C}_6\text{H}_{12}\text{O}_6 + \text{6H}_\text{2}\text{O} + 6\text{O}_2

Checking deforestation means to reduce burning of forests and biomass. This helps to control the emission of green house gases.

Question 25

What is an ozone layer. State the distribution of the ozone layer in the stratosphere.

Answer

Ozone layer is the layer in the earth's atmosphere which contains relatively high concentration of ozone. It absorbs 97-99% of the sun's high frequency U.V. light which is damaging to life on earth. Thus, Ozone layer protects life on earth from harmful solar rays.

Distribution of the Ozone Layer in the Stratosphere:

  1. Ozone layer is mainly located approximately 20-30 kms above the earth's surface.
  2. The thickness of the ozone layer varies geographically and seasonally.
  3. It is less thicker near the equator and larger towards the poles.
  4. It is generally thicker during spring in the northern hemisphere.
  5. Most of the ozone is created over the tropics, but the stratoscopic wind circulation transports it polewards to northern and southern hemispheres.

Question 26

Give balanced equations for formation of ozone molecules from oxygen molecules. What type of reaction takes place, during the formation.

Answer

Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O2] into two oxygen atoms. This reaction is photodissociation or photolysis.

Highly reactive oxygen atom [O] can then react with oxygen molecule [O2] to form ozone [O3]

O2 lightU.V.\xrightarrow[\text{light}]{\text{U.V.}} [O] + [O]

O2 + [O] ⟶ O3 [ozone]

Question 27

How is the 'ozone oxygen cycle' maintained in the stratosphere and state what disturbs the balance, resulting in ozone depletion or destruction, Give balanced equation for the same.

Answer

Ozone is formed in the stratosphere — Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O2] into two atoms. This reaction is photodissociation or photolysis.

Highly reactive oxygen atom [O] can then react with oxygen molecule [O2] to form ozone [O3]

O2 lightU.V.\xrightarrow[\text{light}]{\text{U.V.}} [O] + [O]

O2 + [O] ⟶ O3 [ozone]

How is the ozone oxygen cycle maintained in the stratosphere and state what disturbs the balance, resulting in ozone depletion or destruction, Give balanced equation for the same. Atmospheric Pollution, Simplified Chemistry Dalal Solutions ICSE Class 9.

Ozone is also broken down in the stratosphere — In unpolluted air containing minimal chemical compounds, unstable ozone molecule, in presence of solar radiations may split into molecular oxygen [O2] and an atom of atomic oxygen [O].

The atomic oxygen then combines with another ozone molecule to form two molecules of molecular oxygen.

O3 lightU.V.\xrightarrow[\text{light}]{\text{U.V.}} O2 + [O]

O3 + [O] ⟶ 2O2

How is the ozone oxygen cycle maintained in the stratosphere and state what disturbs the balance, resulting in ozone depletion or destruction, Give balanced equation for the same. Atmospheric Pollution, Simplified Chemistry Dalal Solutions ICSE Class 9.

Thus a continuing process called 'ozone oxygen cycle' is maintained between the amount of ozone [O3] being produced and being destroyed. As a result, the total concentration of ozone remains almost the same.

The balance is disturbed by release of chemicals — such as chlorofluorocarbons containing atomic chlorine and bromine and other free radicals which breaks the ozone molecule causing ozone depletion.

Question 28

Enumerate the damage to humans, animals and plants caused due to ozone depletion.

Answer

Damage to Humans and Animals:

  1. Sun burn and skin cancer
  2. Eye cataract and eye damage
  3. Early aging of skin
  4. Weakening of immune system
  5. Disruption in function of DNA
  6. Severe damage to cells of animals.

Damage to plants:

  1. Retards plant growth.
  2. Inhibits pollen germination
  3. Reduces chlorophyll content
  4. Affects the quality of vegetables
  5. Disrupts ecosystem
  6. Increases harmful mutations

Question 29

Name the chemicals responsible for destruction of the ozone layer. State the main chemical from these chemicals, which is responsible for more than 80% ozone depletion. State the man-made applications which make use of that chemical.

Answer

Chemicals responsible for ozone depletion are :

  1. Chlorofluorocarbons [CFC i.e., CFCl3]
  2. Methyl chloride [CH3Cl]
  3. Methyl bromide [CH3Br]
  4. Carbontetrachloride [CCl4]
  5. Bromofluorocarbons
  6. Methane [CH4]
  7. Nitrous oxide [N2O]

Out of the above chemicals, Chlorofluorocarbons (CFCs) is the main chemical responsible for more than 80% ozone depletion.

Man-made applications making use of Chlorofluorocarbons (CFCs) are:

  1. Aerosol sprays
  2. Coolants in refrigeration and A.C.'s
  3. Drycleaning fluids
  4. Cleansing agents for cleaning electronic components

Question 30

State the role of chlorofluorocarbons in ozone destruction or depletion [no equations required].

Answer

Ozone is broken down by chlorofluorocarbons in the following way:

  1. Chlorofluorocarbons are broken down by ultraviolet radiations in the stratosphere.
  2. By products of the breakdown results in increase in levels of free radicals like atomic chlorine [Cl].
  3. The free radicals reacts with ozone to form ClO[g]. This causes ozone depletion. The Cl free radicals initiate and catalyze a chain reaction capable of breakdown of over 1,00,000 ozone molecules resulting in ozone depletion.

Question 31

Enumerate methods of protecting the ozone layer and preventing it's depletion.

Answer

Ozone layer can be protected by :

  1. Use of products that contain CFC's to be replaced by alternative products.
  2. Substitutes for CFC's have been initiated by scientists and use of HCFC [hydro chlorofluorocarbons] is being considered. Labelling products as CFC free is initiated.
  3. International Treaty [Montreal protocol] was also initiated to prevent ozone depletion.

Unit Test Paper 8 — Atmospheric Pollution

Question 1

Select the correct answer from the choice A, B, C given in each case.

  1. The major pollutant released during burning of fossil fuels.
    A: Carbon monoxide B: Sulphur dioxide C: Hydrogen sulphide

  2. The green house gas which on combustion produces another green house gas.
    A: Nitrous oxide B: Ozone C: Methane

  3. The gas which in presence of U.V. light gives two atoms of the same gas.
    A: Oxygen B: Ozone C: Carbon dioxide

  4. A chemical responsible for ozone depletion.
    A: Methyl acetylene B: Methyl chloride C: Methanol

  5. A renewable source of energy which causes minimum or no pollution.
    A: Fossil fuel B: L.P.G. C: Hydro power.

Answer

  1. B: Sulphur dioxide

  2. C: Methane

  3. B: Ozone

  4. B: Methyl chloride

  5. C: Hydro power

Question 2

Give balanced equations for the following conversions [one or two steps].

  1. Sulphur trioxide to sulphuric acid – a constituent of acid rain.
  2. Nitrogen to nitrogen dioxide – in an internal combustion engine.
  3. Methane to carbon dioxide – a green house gas.
  4. A molecule of ozone to two molecules of oxygen gas.
  5. Oxygen to ozone gas by photolysis.

Answer

  1. Sulphur trioxide to sulphuric acid
    H2O + SO3 ⟶ H2SO4

  2. Nitrogen to nitrogen dioxide in internal combustion engine
    N2 + O2 ⟶ 2NO [At High Temperatures]
    2NO + O2 ⟶ 2NO2

  3. Methane to carbon dioxide
    CH4 + 2O2 ⟶ CO2 + 2H2O + Δ

  4. A molecule of ozone to two molecules of oxygen gas
    O3 lightU.V.\xrightarrow[\text{light}]{\text{U.V.}} O2 + [O]
    O3 + [O] ⟶ 2O2

  5. Oxygen to ozone gas by photolysis
    O2 lightU.V.\xrightarrow[\text{light}]{\text{U.V.}} [O] + [O]
    O2 + [O] ⟶ O3 [ozone]

Question 3.1

Give reasons for the following.

Natural rain water does not have a pH of 7 [i.e. neutral]

Answer

Natural rain water produced in unpolluted air is slightly acidic as CO2 present in traces in unpolluted air dissolves in rain water forming weak carbonic acid [H2CO3].

H2O + CO2 ⟶ H2CO3 [carbonic acid]

Question 3.2

Give reasons for the following.

A catalytic converter in an internal combustion engine reduces pollution.

Answer

The reduction catalyst [Pt/Pd] of the catalytic converter separates the nitrogen atom from NO and NO2 molecules freeing oxygen in the form of O2 molecule.
2NO ⟶ N2 + O2
2NO2 ⟶ N2 + 2O2

Thus, the oxides of nitrogen which are pollutants are converted to free nitrogen by the catalytic converter thereby reducing pollution.

Question 3.3

Give reasons for the following.

In absence of green house gases the surface temperature of the earth is maintained.

Answer

In absence of green house gases the surface temperature on earth is maintained since -

  1. The solar radiation emitted as heat radiation, passes through the clear atmosphere.
  2. It reaches the earth's surface where it is absorbed and retained.
  3. Some of the absorbed heat radiation is reflected back into the atmosphere. [radiation from the earth takes place in two ways - reflected solar radiation and emitted thermal infra red radiation]

Thus, a balance is maintained between the heat energy absorbed by the earth and radiated from the earth and the surface temperature of earth is maintained.

Question 3.4

Give reasons for the following.

The formation of ozone involves a chemical reaction called photolysis.

Answer

Highly energetic ultraviolet radiations from the sun breaks the oxygen molecule [O2] into two oxygen atoms. This chemical reaction is called photodissociation or photolysis.

The highly reactive oxygen atom [O] can then react with oxygen molecule [O2] to form ozone [O3]

O2 lightU.V.\xrightarrow[\text{light}]{\text{U.V.}} [O] + [O]

O2 + [O] ⟶ O3 [ozone]

Question 3.5

Give reasons for the following.

Destruction of ozone layer is harmful for both humans and plants.

Answer

Destruction of ozone layer is harmful for humans because U.V. rays from the sun cause the following damage to humans:

  1. Sun burn and skin cancer
  2. Eye cataract and eye damage
  3. Early aging of skin
  4. Weakening of immune system
  5. Disruption in function of DNA
  6. Severe damage to cells of animals.

U.V. rays also damage plants in the following ways:

  1. Retards plant growth.
  2. Inhibits pollen germination
  3. Reduces chlorophyll content
  4. Affects the quality of vegetables
  5. Disrupts ecosystem
  6. Increases harmful mutations

Question 4

Name or state the following:

  1. An atmospheric pollutant produced during lightening discharge.
  2. A form of wet deposition of acid rain other than rain water.
  3. An atmospheric pollutant responsible for both global warming and ozone depletion.
  4. A green house gas which contains carbon and hydrogen only.
  5. The atom which reacts with oxygen to form ozone.

Answer

  1. NO
  2. Snow
  3. CH4 [methane].
  4. CH4 [methane]
  5. Oxygen atom.

Question 5

Acid rain has adverse effects on the environment. State the effect acid rain has on the following - i.e., A: Increases or B: Decreases

  1. The nutrients present in the soil.
  2. The acidity of the soil.
  3. The fertility of the soil.
  4. The pH of water bodies.
  5. The rate of photosynthesis in plants.

Answer

  1. Decreases
  2. Increases
  3. Decreases
  4. Decreases
  5. Decreases

Question 6

The diagram represents the green house effect.

The diagram represents the green house effect. State why the effect is called 'global warming'. 2. Name a process which (a) releases (b) absorbs – green house gas – CO2. 3. State an advantage of use of C.N.G. over combustion of fossil fuels. 4. Which of the following – biofertilizers or nitrogenous fertilizers reduces the green house gas – N2O. Explain. 5. Does the sea level rise or fall due to global warming. Explain. Atmospheric Pollution, Simplified Chemistry Dalal Solutions ICSE Class 9.
  1. State why the effect is called 'global warming'.
  2. Name a process which (a) releases (b) absorbs – green house gas – CO2.
  3. State an advantage of use of C.N.G. over combustion of fossil fuels.
  4. Which of the following – biofertilizers or nitrogenous fertilizers reduces the green house gas – N2O. Explain.
  5. Does the sea level rise or fall due to global warming. Explain.

Answer

  1. The green house effect results in rise of atmospheric temperature which is not confined to one region but also has a global impact and is termed as 'global warming'.
  2. Process which releases – CO2 is respiration and
    the process which absorbs – CO2 is photosynthesis.
  3. C.N.G. causes minimum pollution. It does not contain lead and lowers maintenance cost as compared to vehicles with other forms of fuels.
  4. Biofertilizers reduce the green house gas N2O as nitrogenous fertilizers release N2O when used in agricultural activities.
  5. The sea level rises due to global warming as increase in temperature melts ice on mountains, ice-caps.
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