Voluntarily giving up throne by king in favour of his son

Answer: Option A

One word substitute is Abdication.

Abdication: an act of abdicating or renouncing the throne.
Resurrection: the action or fact of resurrecting or being resurrected.
Accession: the attainment or acquisition of a position of rank or power.
Renunciation: the formal rejection of something, typically a belief, claim, or course of action.