(i) The formation and destruction of ozone is a regular natural process, which never disturbs the equilibrium level of ozone in the stratosphere. Any change in the equilibrium level of ozone in the atmosphere will adversely affect the life in biosphere in the following ways.
(ii) Depletion of ozone layer will allow more UV rays to reach the earth surface an would cause skin cancer and also decreases the immunity level in human beings.
(iii) UV radiations affects plant proteins which lead to harmful mutation in plant cells.
(iv) UV radiations affect the growth of phytoplankton and as a result ocean food chain is disturbed and it even damages the fish productivity.

(i) The three main components of photochemical smog are nitrogen oxide, ozone and oxidised hydrocarbons like HCHO, CH₂ = CH - CHO and PAN.
(ii) Photochemical smog causes irritation to eyes, skin and lungs. It also increases the chance of asthma.
(iii) High concentration of ozone and NO can cause nose and throat irritation, chest pain, difficulty in breathing
(iv) PAN is toxic to plants, attack younger leaves and cause bronzing and glazing of their surfaces.
(v) It causes corrosion of metals, stones, building materials and painted surfaces.

Water pollution is defined as "The addition of foreign substances or factors like heat which degrades the quality of water, so that it becomes health hazard or unfit to use."
(i) The water pollutants originate from both natural and human activities. The source of water pollution is classified as Point and Non-point source.
(ii) Easily identified source of place of pollution is called as point source.
Example: municipal and industrial discharge pipes.
(iii) Non-point source cannot be identified easily.
Example: agricultural runoff, mining wastes, acid rain, and storm-water drainage and construction sediments.

(a) Causes of water pollution:
(i) Microbiological (Pathogens) : Disease causing microorganisms like bacteria, viruses and protozoa are most serious water pollutants. They come from domestic sewage and animal excreta. Fish and shellfish can become contaminated and people who eat them can become ill. Some serious diseases like polio and cholera are water borne diseases. Human excreta contain bacteria such as Escherichia coli and Streptococcus faecalis which cause gastrointestinal diseases.
(ii) Organic wastes: Organic matter such as leaves, grass, trash etc can also pollute water. Water pollution is caused by excessive phytoplankton growth within water. Microorganisms present .in water decompose these organic matter and consume dissolved oxygen in water.
(iii) Eutrophication: Eutrophication is a process by which water bodies receive excess nutrients that stimulates excessive plant growth ( algae, other plant weeds).This enhanced plant growth in water bodies is called as algae bloom. The growth of algae in extreme abundance covers the water surface and reduces the oxygen concentration in water. Thus, bloom-infested
(b) Biochemical oxygen demand(BOD):
(i) The total amount of oxygen in milligrams consumed by microorganisms in decomposing the waste in one litre of water at 200C for a period of 5 days is called biochemical oxygen demand (BOD) and its value is expressed in ppm.
(ii) BOD is used as a measure of degree of water pollution. Clean water would have BOD value less than 5 ppm whereas highly polluted water has BOD value of 17 ppm or more
(c) Chemical wastes:
(i) A whole variety of chemicals from industries, such as metals and solvents are poisonous to fish and other aquatic life
(ii) Some toxic pesticides can accumulate in fish and shell fish and poison the people who eat them. Detergents and oils float and spoil the water bodies. Acids from mine drainage and salts from various sources can also contaminate water sources.
Harmful effcts of chemical water pollutants:
(i) Cadmium and mercury can cause kidney damage.
(ii) Lead poisoning can leads to the severe damage of kidneys, liver, brain etc. it also affects central nervous system
(iii) Polychlorinated biphenyls (PCBs) causes skin diseases and are carcinogenic in nature.

Health effects of particulate pollutants:
(i) Dust, mist, fumes,etc., are air borne particles which are dangerous for human health. Particulate pollutants bigger than 5 microns are likely to settle in the nasal passage whereas particles of about -10 micron enters the lungs easily and causes scaring or fibrosis of lung lining. They irritate the -lungs and causes cancer and asthma. This disease is also called pneumoconiosis. Coal miners may suffer from black lung disease. Textile workers may suffer from white lung disease.
(ii) Lead particulates affect children's brain, interferes maturation of RBCs and even cause cancer.
(iii) Particulates in the atmosphere reduce visibility by scattering and absorption of sunlight. It is dangerous for aircraft and motor vehicles.
(iv) Particulates provide nuclei for cloud formation and increase fog and rain.
(v) Particulates deposit on plant leaves and hinder the intake of CO₂ from the air and affect photosynthesis.

(i) Industrial activities have been the biggest contributor to soil pollution especially the mining and manufacturing activities.
(ii) Industrial wastes include cyanides, chromates, acids, alkalis and metals like mercury, copper, zinc, cadmium and lead.
(iii) These industrial wastes in the soil surface lies for a long time and makes it unsuitable for use.

Greenhouse effect is defined as the heating up of the earth's surface due to trapping of infrared radiations reflected by earth's surface by the CO₂ layer in the atmosphere.

(i) Air pollutants exists in two major forms namely:
(a) Gaseous air pollutants
(b) Particulates
(ii) Gaseous air pollutants: Oxides of sulphur, oxides of nitrogen, oxides of carbon and hydrocarbons are the gaseous air pollutants.
(iii) Particulate pollutants: Particulate pollutants are small solid particles and liquid droplets suspended in air. Example: dust, pollen, smoke, soot, aerosols

1. The tolerable limit of fluoride ions in drinking water is one ppm or 1 mg dm^-3
2. Higher concentration is harmful to bones and teeth.

(i) Carbon monoxide (CO) combines with, haemoglobin (Hb) of the RBCs about 300 times more readily than oxygen to form carboxy haemoglobin complex.
Hb + CO ⇌ HbCO
(ii) Thus, Hb will not be able to combine with oxygen to for oxyhaemoglobin complex.
(iii) Hence the transport of oxygen to different body cells does not occur (stops). '

(a) Eutrophication : When the growth of algae increases in the surface of water, dissolved oxygen in water is greatly reduced. This phenomenon is known as eutrophication. Due to this growth of fishes gets inhibited.
Pneumoconiosis : It is a disease which irritates lungs. It causes scarring or fibrosis of the lungs.
(b) 

(i) Traditional route : This method involve two steps- Carcinogenic benzene reacts with ethylene to form ethyl benzene. After that ethyl benzene undergoes dehydrogenation using Fe₂O₃ / Al₂O₃ to give styrene.
(ii) Greener route : To avoid carcinogenic benzene, greener routes to start with cheaper and environment friendly xylene

(i) The great smog of London (1952) was an instance of severe air pollution that affected the London from 5th December-9th of December, 1952 and then dispersed quickly when the whether changed.
(ii) It causes major disruption by reducing the visibility and even penetrating indoor areas.
(iii) Government medical reports estimated that 4000 people had died as a direct result of smog and 100,000 were made will by the smog effect on their respiratory tract.

(i) Oxides of nitrogen are produced during high temperature combustion processes, by oxidation of nitrogen in air and it is formed the combustion of fuels such as coal, diesel and petrol.
(ii) N₂ + O₂ \(\underrightarrow { >{ 1210 }^{ o }C } \) 2NO
2NO + O₃ \(\underrightarrow { 1100^{ o }C } \) 2NO₂
NO + O₃ ⟶ NO₂ + O₂
(iii) The oxides of nitrogen are converted into nitric acid which comes down in the form of acid rain. They also form reddish brown haze in heavy traffic.
(iv) Nitrogen dioxide potentially damage plant leaves and retard photosynthesis.
(v) O₂ is a respiratory irritant and it can cause asthma and lung injury

(i) Impact on human:
Exposure to UV radiation lead to ageing of skin, cataract, sun bum and skin cancer.
(ii) Impact on aquatic life:
Many phytoplanktons are killed and the productivity of fishes are damaged.
(iii) Impact on plant life:
The plant proteins get easily affected by UV radiation.
It also increases evaporation of surface water through the stomata of the leaves and decrease the moisture content of the soil.