Give reasons for the following observations:(a) Air holes of a gas burner have to be adjusted when the vessels being heated get blackened by the flame.
(b) Use of synthetic detergents causes pollution of water.

(a) The gas stove used in our homes comprises burners with tiny holes in them so as to let insufficient oxygen required for the fuel to burn. When there is sufficient oxygen, the fuel will burn completely with a blue flame.

If the fuel fails to burn completely, a sooty flame is produced (due to the incomplete combustion) which blackens the bottom of the vessel. Therefore, the air holes in the gas burner need to be adjusted so that the burner gets enough oxygen to burn the fuel completely.

(b) Some detergents like synthetic detergents are not biodegradable, as they can not be decomposed by microorganisms such as bacteria. Hence, they pollute water bodies like rivers and lakes.