(a)–(iii), (b)–(iv), (c)–(ii), (d)–(i)

a) Sulphur dioxide (SO₂) is one of the gases that are responsible for causing acid rain. The other gas is Nitrogen dioxide.

b) Carbon dioxide is one the 5 main greenhouse gases. The other three are: water vapor, methane, nitrous oxide and ozone.

c) Carbon monoxide reduced oxygen carrying capacity of the blood. Oxygen has hemoglobin which carries oxygen. Hemoglobin however, has a higher affinity for Carbon monoxide which means carbon monoxide can bind to hemoglobin more easily than oxygen. So when carbon monoxide is present, hemoglobin binds to it rather than to oxygen and reduces the amount of oxygen being carried by the blood.

d) CFCs or chlorofluorocarbons damage the ozone layer. CFCs are broken down by the UV radiations and release chlorine atoms. These chlorine atoms destroy the ozone.