The answer is: C
Explanation
The correct option is C: remains valid.
This is because the Hindu Marriage Act, 1955, which prohibits bigamy and polygamy for Hindus, is not retrospective in its application. It means that it does not affect the validity of marriages that were contracted before the commencement of the Act. Therefore, a bigamous marriage that was contracted before the Act came into force remains valid, unless it is challenged by the aggrieved party on other grounds.
However, if a Hindu contracts a bigamous marriage after the Act came into force, then such a marriage is void ab initio, meaning it is invalid from the very beginning. Moreover, bigamy is also an offence under Sections 494 and 495 of the Indian Penal Code, 1860, and is punishable with imprisonment or fine or both.