Mohan and his sister's daughter Kriti are Hindus. Assuming all other statutory conditions for marriage…

Uncle and niece are within the degrees of prohibited relationship under section 3(g)(iv) of the Hindu Marriage Act, 1955, but section 5(iv) allows such a marriage where the custom or usage governing each of them permits it; any applicable sapinda bar under section 5(v) has the same custom exception. The marriage is therefore "Valid if a legally recognised custom or usage governing each party permits the marriage"; otherwise it is void under section 11.