The correct option is A 12 years
Becoming an ascetic at the age of 30, Vardhaman Mahavira practised the most rigorous asceticism for the next twelve years. In the thirteenth year, at the age of 42. he attained "Kaivalya" i.e. the supreme knowledge and final deliverance from the bonds of pleasure and pain. Hence, he was called "Kevalin". He sat under a sal tree on the bank of river Riju Palik or Riju Kaa in Jambhika near Vaishali for the attainment of Kaivalya.