Ozone shield is a part of stratasphere in which the concentration of ozone is very high. It is called as ozone shield because it prevents the sun's UVradiations entering the earth atmosphere and in this way protects the living beings from harmful effects of these radiations.
Stratospheric ozone deplition results in the impairment of photosynthetic machinary in green plants which increases CO₂ concentration and result in global warming and skin cancer and catract in humans. CFCs and CH₂ gases cause damage to ozone shield.

The green house effect is a naturally occurring phenomenon that is responsible for heating of earth and atmosphere, Green house gases like CO₂ absorb the infrared radiation of the sun and prevent it from escaping. 
A green house which is like a small glass house is used for growing plants during winter as it provides the appropriate temperature to the plants, as the glass also prevents the IR radiation from escaping thereby increasing the temperature inside.

Events that reduce biological oxygen demand of primary effluent.
The amount of oxygen required for microbial breakdown of biodegradable organic matter is called BOD. It is higher in polluted water and lesser in drinking water. Primary treatment is physical treatment. The supernation of settling tank is called effluent.  It is put into biological treatment involving microbial decomposition fine organic matter. It is further heated by trickling filter and activated sludge method.

Yes, the water become septic if the dissolved oxygen drops to zero. Organic pollution (biodegradable) is an example.

1. As the exhaust passes through the catalytic converter, the unburnt hydrocarbons are converted into carbon dioxide and water; carbon monoxide and nitric oxide are converted into carbon dioxide and nitrogen gas.
2. The metals include rhodium.platinum and palladium.

(i) In a national park, a track of land (core zone) is reserved and maintained solely for wild life conservation, and operations such as plantations, cultivation, grazing are not allowed. Private ownership rights and habitat manipulation are also not permitted in this zone.
(ii) Kazipranga National Park and Kanha National Park.
(iii) Amitabh's uncle maintained his nephew's curiosity to know about surroundings, wildlife and their importance in our life.

An electrostatic precipitator. It removes over 99% particulate matter present in the exhaust from a thermal power plant. It has electrode wires and a stage of collecting plates. The electrode, wires are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles and give them a net negative charge within a very small fraction of a second. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.

Biological Magnification is the phenomenon in which harmful chemical/pollutants get accumulated in the tissues of living organisms in increasing concentrations at successive trophic levels as they travel along the food chain.
1. When DDTwas used in a lake in USA to control mosquitoes, it was found that the phytoplanktons came to possess 800 times more DDT than that in the water of the lake.
2. Zooplanktons had about 5 times greater amount of DDT than phytoplanktons.
3. The fish population contained 9-40 times more DDT than zooplanktons.
4. The fish-eating birds had 25 times more than fish.

Causes of global warming:
(i) Deforestation
(ii) Burning of fossil fuels
(iii) Excess use of nitrogenous fertilisers
(iv) Increased amounts of greenhouse gases(CO₂, CH₄, CFCs, N₂O).
It is a warning to humans because
(i) it leads to deleterious changes in the environment resulting in odd climatic changes.
(ii) it can lead to melting of polar ice caps and ice caps on mountain tops and result in a rise in sea level which can submerge many coastal areas.

(i) Deforestation by clearing forest area for cultivation forest area for cultivation of crops, grazing the cattle, felling of trees for timber etc.
(ii) Overgrazing, that leads to soil erosion in the absences to hydrological cycle, by deforestation.

(a) Mohit will give following reasons:
(i) CNG bums most efficiently, unlike petrol or diesel, in the automobiles and very little of it is left unburnt.
(ii) CNG is cheaper than petrol or diesel, cannot be siphoned off by thieves and adulterated like petrol/diesel. 
(b) Mohit shows: concern towards environment, a areness towards sustainable development.
(c) Phasing out of old vehicles, use of unleaded petrol, use of low sulphur petrol/diesel, use of catalytic converters in vehicles and application of strigent pollution level norms for vehicles.

(a) Ozone layer in the stratosphere acts as a shield to absorb the ultraviolet radiation from the sun, which is highly injurious to living organisms.
1. Chlorofluorocarbons (CFCs), from refrigerators and aerosol sprays, degrade the ozone layers.
2. The UV rays act on the CFCs and release CI atoms; which degrade ozone to molecular oxygen.
(b) In the absence of ozone, which absorbs the ultraviolet radiation, the UV rays reach the earth and cause the following ill-effects.
(i) UV-B damages DNA and causes mutation in living organisms.
(ii) It causes ageing of skin, damage to skin cells and various types of skin cancers.
(iii) A high dose of UV-B causes inflammation of cornea, called snow-blindness, cataract and even permanent damage to cornea.