1.Reasons: Carbon forms a large number of compounds. Two properties of carbon that
help it to form so many compounds is:
Catenation (The ability of carbon to combine with other atoms of carbon).
It forms strong covalent bonds with various elements like oxygen, nitrogen, chlorine, bromine, etc.
2.Blackening (deposition of unburnt carbon particles) of the cooking vessels show that incomplete combustion of the gas is taking place. As combustion is not taking place, the maximum amount of energy that can be obtained from the fuel cannot be obtained i.e., gas is being wasted. Limited supply of air results in the incomplete combustion of saturated hydrocarbons. Hence, the air holes of a gas burner have to be adjusted, so that, a sufficiently oxygen-rich mixture is burnt and a clean blue flame is obtained.
3.Synthetic detergents are non-biodegradable in nature and cannot be decomposed by micro-organisms. Therefore, they remain as they are for a long time in nature, thereby, causing water pollution. Hence, the use of synthetic detergents causes pollution of water.