(i) Intermixing of particles 9ases or liquids spontaneously is called diffusion. Liquids diffuse at a slower rate as compared to gases.
(ii) Ammonia gas will reach first to a person in the centre of the laboratory because it is lighter than hydrochloric acid. 
(iii) The phenomenon of diffusion of gases is very useful in daily life. As a result of diffusion, the poisonous effect of the gases gets slowly diluted

Technology has now been developed to produce electricity from the garbage. Garbage is cultured with bacterial species for producing methane commonly known as biogas. It can be used to produce electricity.

Triazines.

H₂SO₄, HNO₃ and HCL.

If domestic waste in a city is not properly managed, it may finds its way into sewers or may be eaten up by the cattle. The non-biodegradable waste like polythene bags, metal scrap etc., choke the sewers. The polythene bags if swallowed by the cattle can result into their death. Similarly, if industrial waste is not properly managed, it will cause pollution of the air, soil and water.

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

Carbon monoxide is poisonous because it combines with haemoglobin of R.B.C. to form carboxyhaemoglobin as.
CO + Haemoglobin ⇌ Carboxyhaemoglobin
It inhibits the transport of oxygen to different parts of the body. Thus the body becomes oxygen-starved.

Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air. The major gaseous and particulate pollutants present in the troposphere are
(i) Gaseous air pollutants These are oxides of sulphur, nitrogen, carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants. 
(ii) Particulate pollutants These are dust, mist, fumes, smoke, smog, etc.
Gaseous air pollutants
(a) Oxides of sulphur These are produced when sulphur containing fossil fuel is burnt. SO₂ gas is poisonous to both animals and plants.
(b) Oxides of nitrogen These are produced by the reaction of nitrogen and oxygen at high altitudes when lightning strikes.
\( \mathrm{N}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \stackrel{1483 \mathrm{~K}}{\longrightarrow} 2 \mathrm{NO}(\mathrm{g})\)
\(2 \mathrm{NO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{NO}_{2}(g) \)
\(\mathrm{NO}(g)+\mathrm{O}_{3}(g) \longrightarrow \mathrm{NO}_{2}(g)+\mathrm{O}_{2}(g) \)
(c) Hydrocarbons Incomplete combustion of fuel used in automobiles is the major source for the release of hydrocarbons. These are carcinogenic and cause cancer. They also harm plants.
(d) Oxides of carbon Carbon monoxide is one of the most serious air pollutants. It is highly poisonous to living beings because it blocks the supply of oxygen to the organs and tissues. It is produced due to the incomplete combustion of carbon. Carbon dioxide is the main contributor for global warming. It is released in"l:o the atmosphere by respiration, burning of fossil fuels and by decomposition of limestone during cement manufacturing.

Chlorofluorocarbons are introduced into the atmosphere from aerosol sprays in which they function as propellants and from refrigerating equipment in which they act as coolants. It is also used as solvents.
It has very long life and stay in the atmosphere for years and ultimately reach the upper layer of the atmosphere where it decomposes in presence of UV-radiation of the sun.
\({ CF }_{ 2 }{ Cl }_{ 2 }\underrightarrow { hv } ^{ . }{ { CF }_{ 2 }+{ Cl }^{ . } }\)
The active chlorine atoms then destroy the ozone layer.
\({ Cl }^{ . }+{ O }_{ 3 }\longrightarrow { CIO }^{ . }+{ O }_{ 2 }\)
\({ CIO }^{ . }+O\longrightarrow { CI }^{ . }+{ O }_{ 2 }\)
It has been found that one thousand ozone molecules in the stratosphere.

In the stratosphere, ozone is continuously created and destroyed by the sun's radiations. This results in an equilibrium concentration of ozone. In 1980s atmospheric scientists working in Antartica reported about the depletion of ozone layer commonly known as ozone hole over the South Pole.

Pesticides These substance are used to kill or block the reproductive processes of pests. These are basically synthetic toxic chemicals with ecological repercussions. Their accumulation in higher animals causes serious metabolic and physiological disorders. DDt, aldrin, dieldrin, organophosphates and carbonates are some examples of pesticides.
Herbicides These are weed killers i.e. they kill unwanted herbs growing along with crops e.g. sodium chlorate (NaCIO₃) and sodium arsenite (Na₃AsO₃). These are toxic to mammals. Some herbicides cause birth defects. Now a days triazines, better herbicides are used for the corn fields.

Yes, polluted water is the water whose quality has been degraded by the addition of substance such as chemical effluents, metal residues, sewage, oil, fertilisers, detergents, etc.
It can be controlled by the following methods.
(i) Industrial waste discharge from paper, fertilisers, should not be allowed to get mixed in water bodies such as river, lakes, etc.
(ii) Non-biodegradable detergents should be used for cleaning of clothes
(iii) The ph of water should be checked.
(iv) Excessive use of fertilisers should be prevented.
(v) oils spills should be avoided as much as possible
(vi) Domestic waste water should be properly discharged and treated.
(vii) Avoid the use of DDT, malathion at home.
(viii) Waste water should be treated in sewage treatment plant.