(i) To prevent the pJssage of particulates of smoke in the atmosphere.
(ii) Electrophoresis.
(iii) 'Coal contains impurities of sulfur, arsenic, lead etc. and therefore, the smoke will contaminate the air. These particles are injurious to health and have to be removed from the smoke.
(iv) The value promoted is a concern for keeping the environment clean and prevent air pollution.

(i) The cell walls of the vegetables have semi-permeable membrane. When the vegetables have dried, the concentration of water inside becomes low. When the dried or shrinked vegetables are placed in water, water enters into the cells due to osmosis. Hence, they swell and return to the original form.
(ii) The process is osmosis. It is defined as the flow of the solvent molecules from the solvent to the solution or from less concentrated solution to a more concentrated solution through a semi-permeable membrane.
(iii) The process will be accelerated with increase of temperature because osmosis becomes faster with increase of temperature.

Many food products are available in the markets in tin cans, which are made from steel with a very thin coating of tin. the thin layer, which is only a few thousands of a millimeter thick, prevents the steel from rusting. If the coating gets scratched, the can will soon corrode. This will allow bacteria from the air to cause food poisoning. Thus, the tin can with scratches have chances of getting spoiled. Hence, the decision of Jayant is justified.

(a) Though D.D.T is a very powerful insecticide for mosquitoes, yet the excessive use of D.D.T has many problems. The use of D.D.T has the following disadvantages:
(i) Many species of insects develop resistance to D.D.T.
(ii) It has a high toxicity towards fish.
(iii) The chemical stability of D.D.T and its fat solubility has problems.
(iv) It is not biodegradable and its residues accumulate in environment and its long term effects could be dangerous.
(v) D.D.T is not metabolized very rapidly by animals rather it gets deposited and stored in fatty tissues. Because of its dangerous effects, its use has been banned in U.S.A in 1973. However, in spite of its dangerous effects, D.D.T is still being used in India because of non-availability of other cheaper insecticides.
(b) Mukesh's suggestion is very important to protect our environment. Because of long-term dangerous side effects of D.D.T., it should not be used to save our environment.

(i) Liberation of hydrogen prevents the formation of FeCI₃. 
(ii) Structure of XeO₃