In Relation puzzle type, mutual blood relations or other information of more than two persons are mentioned and information about any two is mentioned.
A an B are married couple. X and Y are brothers. X is the brother of A.
How is Y related to B ?
A and B are husband and wife. Since X and Y are brothers, and X is the brother of A, Y is also the brother of A.
Thus, Y is the brother-in-law of B.
Hence, the answer is (a).