Other gases like CFCs, Ozone, water vapour and nitrous oxide also show green house effect.

Phosgene (COCl₂) is a poisonous and suffocating volatile liquid. Release of methyl isocyanate in industrial accident of Bhopal was the main reason of Bhopal gas tragedy.

Eutrophication is a natural process which literally means well nourished or enriched. It is a natural state in many lakes and ponds which have a rich supply of nutrients.Eutrophication become excessive, however when abnormally high amount of nutrient from sewage,fertilizers, animal wastage and detergent,enter streams and lakes causes excessive growth or blooms of microorganisms. With increasing eutrophication, the diversity of the phytoplankton community of a lake increases and the lake finally becomes dominated by blue - green algae.

Noise level upto 64 dB (decibel) is well tolerated.Prolonged exposure to noise level to 80 dB or more leads to loss of hearing ability, fatigue,nervousness,fever, hypertension, gastric disorder, increase in cholesterol level and dilation of pupil of the eye. As the jet aeroplanes have the noise upto 150-160 dB, the inhabitants in the vicinity of busy airports are likely to experience above health hazards. Maximum noise level is recorded in rockets, i.e., 180 dB.

Ozone layer acts as a shield and does not allow ultraviolet radiation from sun to reach earth. It does not prevent infra-red radiation from sun to reach earth.Thus option (c) is wrong statement and so it is the correct answer.

The ideal value of D.O for growth of fishes is 8 mg/ℓ. 7mg /ℓ is desirable range, below this value fishes get susceptible to disease. A value of 2 mg/ℓ or below is lethal for fishes.

Green house gases such as CO₂, ozone, methane,the chlorofluorocarbon compounds and water vapour forma thick cover around the earth which prevents the IR rays emitted by the earth to escape. It gradually leads to increase in temperature of atmosphere.

[Many organic substances break up into simpler substances by taking up dissolved oxygen in presence of some bacteria. As they continue, dissolved oxygen,runs short for aquatic life, which is then badly affected.Moreover many harmful products are formed].