Environmental pollution is the effect of undesirable changes in our surroundings that have harmful effects on plants, animals and human beings. Even small amount of pollutants in air become significant. Some pollutants are biodegradable, e.g., discarded vegetables which rapidly break down by natural processes. DDT, plastic material, heavy metals, many chemicals, nuclear waste remain in environment for long time, are difficult to remove. Virus, bacteria cause diseases. Some of them are air borne. Some microorganisms get contaminated with water. Excessive use of fertilizers pesticides, insecticides cause soil pollution. Each household cleaning chemicals are harmful for children. Green chemistry can help to reduce pollution of air, water and soil.
(a) When does rain become acid rain?
(b) BOD, biological oxygen demand measure of organic material present in water. If BOD value is greater than 17 ppm what does it indicate? What is ideal value?
(c) Why should jet aeroplanes not fly in stratosphere?
(d) If there is enhance algae growth in water, what is its cause?
(e) Which is more suitable for dry cleaning and why?

The table gives the tolerable limits up to which they are permitted in water according to international standards. Study the table and answer the questions based on table and related studied concepts.

(a) Name two most harmful heavy metals present in water.
(b) What is effect of higher cone  of \(\mathrm{SO}_{4}^{2-}\) ?
(c) Which disease is caused by excess of \(\mathrm{NO}_{3}^{-}\) ?
(d) What is use of F^- ions?
(e) Which metal is safe among aU metals given in the table?
(f) Is drinking distilled water good for health?
(g) Which is better bleaching agent out of chlorine and H₂ O₂?