a) 1. Alkanes are saturated hydrocarbons with least reactivity.
2. Therefore they are called paraffins.
3. Parum = little and affins = affinity.
b) 1. A reaction in which one atom or a group of atoms in a given compound is replaced by other atom or group of atoms is called a substitution reaction.
2. Alkanes have single bonds and undergo substitution reactions.
3. For example : Methane (CH ) reacts with chlorine in the presence of sunlight.