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

It is a kind of smog formed in warm, dry and sunny climate. It is formed when sunlight is absorbed by SO₂ oxides of nitrogen and hydrocarbons.
It act as an oxidising agent.
Effects of photochemical smog
(i) It produces irritation in eyes and also in respiratory system.
(ii) It can damage many materials such as metals, stones, building materials etc.
(iii) NO₂ present in photochemical smog gives it brown colour which reduces the visibility.
(iv) It is harmful to fabrics, crops and ornamental plants.
Control of photochemical smog
(i) By using catalytic converters in automobiles.
(ii) By spraying certain compounds into the atmosphere which generate free radicals that can easily combine with the free radicals that initiates the reaction forming toxic compounds of photochemical smog.
(iii) Certain plants such as Pinus, Juniparus, Pyrus could be also helpful in this matter.

Depletion of ozone layer creates some sort of holes in the blanket of ozone which surrounds us in the atmosphere and this is known as ozone hole
(i) With the depletion of the ozone layer, UV radiations filters into the troposphere which leads to ageing of skin, cataract, sunburn, skin cancer etc.
(ii) By killing many of the phytoplanktons, it can damage the fish productivity.
(iii) Evaporation rate increases through the surface and stomata ofleaves which can decrease the moisture content of the soil.

Acetaldehyde is commercially prepared by one step oxidation of ethene in the presence of ionic catalyst in aqueous medium with 90% yield.

(i) Traditional route : This method involve two steps- Carcinogenic benzene reacts with ethylene to form ethyl benzene. After that ethyl benzene undergoes dehydrogenation using Fe₂O₃ / Al₂O₃ to give styrene.
(ii) Greener route : To avoid carcinogenic benzene, greener routes to start with cheaper and environment friendly xylene