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(i) Classical smog is initiated by a mixture of SO₂ , particulates and high humidity in the atmosphere in cold conditions. A fog of H₂SO₂ droplets formed condenses on the particulates to form the smog. It is of reducing nature. The gases released by automobiles and factories are not responsible for classical smog.

(i) Ozone is not responsible for green house effect.

(i) In the presence of insufficient oxygen in the closed room,coke burns to produce a lot of carbon monoxide.It combine with haemoglobin to form carboxyhemoglobin. Thus,the function of haemoglobin to carry oxygen to diff. Body cell is inhibited this causes oxygen starvation leading to coma and death. 

(ii) When motor fuel burns, they produces high temp. At which N₂ and O₂ of the air combine to form oxides of N₂ which are toxic and affect respiratory system and damages the lungs. 

(iii) SO₂ enters into atmosphere through volcanic eruption and through combustion of sulphur containing coal and fuel oil in thermal power plants.Its presence around the plants slows down the formation of chlorophyll resulting in loss of green colour. it dissolves in rain water forming sulphuric acid which attack marbel building like taj in Agra.

(d) O₃  It is present in stratosphere whereas others are present in troposphere.

The particulates from air can be removed by using electrostatic precipitators, gravity settling chambers, wet scrubbers or by cyclone collectors. These techniques are base on washing away or settling of the particulate matter.

(c) Acid rain : HCl + HNO₂

Correct answer is (c) SO₂

Earth’s atmosphere is a layer of gases retained by earth’s gravity. it contains roughly 78% Nitrogen, 21% Oxygen. 0.93% Argon, 0.04% Carbon dioxide. traces of other gases and little amount of water vapour. This mixture is commonly known as air.

Pesticides are those chemicals which are used to destroy pests, rats, parasites and fungi.

(i) enhanced growth of algae.
(ii) decrease in amount of dissolved oxygen in water.

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

BOD stands for biochemical oxygen demand whereas COD stands for chemical oxygen demand.

Methyl isocyanate gas caused Bhopal gas tragedy. Its formula is 

CH3 – N = C = O

BOD stands for Biochemical oxygen demand whereas COD stands for chemical oxygen demand.

The process of removing dissolved oxygen from water by microorganisms in order to oxidise organic matter of sewage is called deoxygenation.

BOD: It is amount of oxygen required by bacteria to decompose organize wastes present in water. 

COD: It is the amount of oxygen (in ppm) required to oxidize the contaminants. COD is determined by using chemical oxidizing agent K₂Cr₂O₇.

(i) rich in dissolved oxygen.

Photochemical smog: It is formed as a result of photochemical reaction between SO₂, oxides of nitrogen and hydrocarbons in the presence of sunlight. It is also called Los Angeles smog. It is formed around mid-day in summer months.

Harmful effects of photochemical smog:

(i) Aldehydes and PAN components of smog cause irritation of eyes and affect the respiratory tract of human beings.

(ii) Ozone causes cracks in rubber materials and is harmful to fabrics.

Biochemical oxygen demand (BOD): 

• The total amount of oxygen (in milligrams) consumed by microorganisms in decomposing the waste in one litre ut water at 20°C for a period of 5 days is called biochemical oxygen demand (BOD). 
• its value is expressed in ppm.
• BOD is used as a measure of degree of water pollution.
• BOD is only a measurement of consumed oxygen by microorganims to decompose the organic matter. Clean water would have BOD value less than 5 ppm

Chemical ox gen demand (COD):

• Chemical oxygen demand is defined as the amount of oxygen required by the organic matter in a sample of water for its oxidation by a strong oxidising agent like K₇Cr₂ O₇ in acidic medium for a period of 2 hours. 
• Its value is expressed in mg / litre. 
• COD is a measure of amount of organic compounds in a water sample. 
• COD refers to the requirement of dissolved oxygen for both the oxidation of organic and inorganic constituents
• Clean water would have COD value greater than 250 mg/ litre.

2. Viable and non-viable particulate pollutants Viable pollutants:

• The viable particulates are small size living organisms such as bacteria, fungi. moulds, algae which are dispersed in air. 
• They are all organic particulates. 
• They contain living organisms. 
• Eg. ftingi, bacteria, algae, moulds. Viable particles are the particles with at least one microorganism affecting the sterility of the product.

Non-viable pollutants:

• The non-viable particulates are small solid particles and liquid droplets suspended in air. 
• They are all inorganic particulates. 
• They contain non-living organisms.
• Eg. Smoke, dust, mist, fumes. 
• Non-viable particles are the particles without microorganisms but act as transporting agent for viable particles.

1. Particulate pollutants are small solid particles, and liquid droplets suspended in air. 

Examples: dust, pollen, smoke, soot and liquid aerosols.

2. Types of Particulates: 

Particulates in the atmosphere may be of two types: 

• viable particulate and 
• non-viable particulate. 

3.The viable particulates are small size living organisms such as bacteria, fhngi, moulds and algae which are dispersed in air.

4. The non-viable particulates are small solid particles and liquid droplets suspended in air. There are four types of non-viable particulates in the atmosphere. 

They are 

(a) Smoke 

(b) Dust 

(c) Mist

(d) Fumes 

5. Smoke: 

Smoke particulate consists of solid particles formed by combustion of organic matter. 

For example, cigarette smoke, oil smoke, smokes from burning of fossil fuels, garbage and dry leaves.

 6. Dust: It is composed of fine solid particles produced during crushing and grinding of solid materials. 

For example, sand from sand blasting, saw dust from wood works and fly ash from power generating units.

7. Mist: 

They are formed by particles of sprayed liquids and condensation of vapours in air. For example, sulphuric acid mist, herbicides and insecticides sprays can form mists.

8. Fumes: 

They are obtained by condensation of vapours released during sublimation, distillation, boiling and calcination and by several other chemical reactions. 

For example: organic solvents, metals and metallic oxides.

Danger associated with CO and CO₂ & health hazards to human body 

(a) Carbon monoxide binds with haemoglohin and form carboxyhaemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced. This oxygen deficiency results in headache, tension, dizziness, loss of consciousness, blurring of eyesight and cardiac arrest.

(b) Increase in CO₂ level in the atmosphere is responsible for global warming. It causes headache and nausea.

The alternate solvent used insted of tetrachioroethYlefle in dry cleaning is Liquefied CO₂

Pesticides are those chemicals which are used to destroy pests, rats and parasite fungi.

Pesticides are basically synthetic toxic chemicals with ecological repercussions.

Ex: DDT, Aldrin etc. 

Solvents like tetrachioroethylene is used in dry cleaning of clothes, pollute the ground water and are carcinogenic. In place of tetrachloroethylene liquefied CO₂ with suitable detergents an alternate solvent used. Liquefied CO₂ is not that much harmful for the groundwater. Nowadays H₂O₂ is used for bleaching clothes in laundry that give better results and utilises less water.

(i) Detergent are non-biodegradable and they cause water pollution. 

(ii) They inhibit oxidation of organic substances present in waste water because they form a sort of envelope around them. 

(iii) They form stable foam in rivers which extend over several hundred meters of the river water.

Pesticides are substances which are used to kill or block the reproductive process of unwanted organisms. 

The three main categories of pesticides are:

(i) Insecticides: These are used to control insects and curb diseases and protect crops. 

(ii) Herbicides: These are used to kill weeds .Example- sodium chlorate (NaClO₃), sodium arsinite(Na₃AsO₃) 

(iii) Fungicides: These are used to check the growth of fungi. Example-methyl, mercury. 

(a) Water pollution is defined as the contamination of water by foreign substances which make it harmful for health of animals or plants or aquatic life and make it unfit for domestic, industrial and agricultural use. 

Oxygen gets into water through two sources:

(i) Dissolution of oxygen at the surface of water from the atmosphere

(ii) From photosynthesis of aquatic plants. 

(b) The measurement of BOD takes 5 days while measurement of COD does not take much time. Hence, COD is preferred over BOD.

(a) Mists: Mists are produced by particles of spray liquids and the condensation of vapours in air.

(b) Smoke: They are very small soot particles produced by burning of organic matter.

(c) Fumes: These are condensed vapours. Fumes of metals are well known particulates of this type.

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

The total amount of oxygen (in milligrams) consumed by microorganisms in decomposing the waste in one litre of water at 20°C for a period of 5 days is cal Led biochemical oxygen demand (BOD) and its value is expressed in ppm.

BOD is a measure of Organic pollutant in water.

1. Pesticides are the chemicals that are used to kill or stop the growth of unwanted organims. But these pesticides can affect the health of human beings.

Pesticides are classified as 

(a) insecticides, 

(b) Fungicides and 

(c) Herbicides.

(a) Insecticides: 

Insecticides like DDT, BHC, Aidrin can stay in soil for a long period of time and are absorbed by soil. They contaminate root crops like carrot, radish. 

(b) Fungicides: 

Organomercury compounds dissociate in soil to produce mercury which is highly toxic. 

(c) Herbicides: 

They are used to control unwanted plants and are also known as weed killers. Eg, Sodium chlorate, sodium nitrate. They are toxic to mammals.

(i) Pesticides: Those which are used to kill pests, insects which are harmful for the crops, e.g., Aldrin, Dieldrin B.H.C. etc., 

(ii) Herbicides: Those chemicals which are used to destroy weeds i.e., unwanted plants are called herbicides, e.g., sodium chlorate, sodium arsenite etc.

Solvents used to dry clean clothes are usually chlorinated compounds such as tetra chloroethylene (CCl₂=CCl₂) which is a potential human carcinogen. These chlorinated compounds also have serious environmental consequences such as greenhouse effect, ozone depletion, water pollution, etc. The use of liquefied carbon dioxide with a suitable detergent for dry cleaning will not be completely safe from the point of view of pollution but will be less harmful. 

Pesticides are substances which are used to kill or block the reproductive process of unwanted organisms.

The three main categories of pesticides are:-

(i) Insecticides: These are used to control insects and curb diseases and protect crops.

(ii) Herbicides: These are used to kill weeds. Example- sodium chlorate (NaCIO₃), sodium arsenite (Na₃AsO₃)

(iii) Fungicides: These are used to check the growth of fungi. Example-methylmercury

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

(iii) Both A and R are not correct.

(a) The clean water would have a BOD value of more than 5 ppm

Correct answer is (d) (iv)

 Pesticides are organic compounds which are used to protect plants from pests. These are mild poisons. These pesticides stick to the plants and also flow into lakes along with the rain water. Rearing fishes when consume these plants as their food the poisonous pesticides accumulate in the tissues of fishes. Thus, these fishes are not fit for human consumption. 

Carbon dioxide is a natural constituent of atmosphere and is vital for all forms of plant life. It forms about 0.033% by volume of atmosphere. It helps to maintain the temperature of the earth required for the living organisms. A balance of CO₂ is maintained in air because CO₂ is produced from respiration, burning of fossil fuels and decomposition of lime stone but at the same time it is consumed in photosynthesis by plants. However, human activities have disturbed this balance and CO₂ level in atmosphere is in increasing order. This has happened due to deforestation, burning of more of fossil fuels and industrialization. It has been estimated that CO₂ concentration has risen about 25% in the past century. During the past nearly 120 years, the average temperature of the planet has increased by somewhere between 0.4 and 0.8^∘C. Current estimates are that doubling the CO₂ concentration will result in a temperature increase of between 1.0 and 3.5^∘C. The greenhouse effect contribution of CO₂ is 50% and of other trace gases is also about 50%. 

Correct answer is (d) (iv)

(ii) The atmosphere is divided into four major regions:

(i) Troposphere (ii) Stratosphere . (iii) Mesosphere and (iv) Thermosphere Troposphere is the lowest region of the atmosphere.

The discharge of human sewage and organic waste from pulp and paper industry and presence of leaves, grass, trash etc. in water due to run off result in phytoplankton growth. The microorganisms which decompose this organic matter need oxygen. Hence, the amount of oxygen in water of lakes etc. decreases.

NO₂ + UV radiation \(\overset{photolysis}{\rightarrow}\) NO + (O) ..................(i)

O + O₂ ⇌ O₃  ............(ii)

Ozone so formed oxidises NO to NO₂ + O₂

NO + O₃ → NO₂ + O₂ ……(iii)

(O) + Hydrocarbon → RCO \(\overset{O_2}{\rightarrow}\) RCO₃

RCO₃ + Hydrocarbons → CH₂ = O, ketones, etc.

RO₃ + O₂ → RCO₂ + O₃

RCO₃ + NO → RCO₂ + NO₂

RCO₃ + NO₂ → RCO₃NO₂ (PAN)

The presence of excessive O₃, along with aldehydes ketones, PAN constitute photochemical smog.

Control:

(i) Efficient catalytic converters are being developed for fitting in the automobiles so that the emission of nitrogen oxides and hydrocarbons can be prevented.

(ii) Certain chemical compounds are sprayed into atmosphere, which generate free radicals. These free radicals readily react with the free radicals responsible for the formation of photochemical smog and nullify their effect.

(iii) Toxic nature causes coughing, wheezing, bronchial constrictions and irritation to respiratory mucous system.

Presence of excessive algal growth shows that water contains a lot of phosphate due to inflow of fertilizers, etc from the surroundings. Hence, such a sample of water is polluted.

If domestic waste in a city is not properly managed, it may find its way into sewers or may be eaten up by the cattle. The non-biodegradable wastes like polythene bags, metal scrap etc. choke the sewers. The polythene bags, if swallowed by the cattle, can result into their death. Similarly, if industrial waste is not properly managed, it will cause pollution of the air, soil and water.