What is the meaning of 'mother tongue' in the context of Census of India?

the language spoken in childhood by the person's mother to the person. the language spoken in childhood by the person's father to the person. the language spoken in childhood by the person's mother and father to the person. the language spoken in childhood by the person's mother or father to the person.

the language spoken in childhood by the person's mother to the person.

The census defined Mother Tongue as "the language spoken in childhood by the person's mother to the person. If the mother died in infancy, the language mainly spoken in the person's home in childhood will be the mother tongue.