Mohan said to Neha, “Your only brother’s son is my wife’s brother”. If Mohan…

In a blood-relation puzzle, first convert every sentence into a direct parent-child or sibling link -- a small family tree -- instead of reasoning from the wording alone. A statement of the form "X's brother's son is Y's brother" tells you that this son and Y are siblings, so they share the same father, and that shared father must be X's brother. Read the relation that is actually asked for off that tree, not off the sentence.

1. Mohan's wife is Rita (given).

2. Mohan tells Neha: “Your only brother’s son is my wife’s brother” -- so Neha's (only) brother's son is Rita's brother.

3. That person is Rita's brother, so he shares the same father as Rita -- call that shared father X. So X is Rita's father.

4. The same person is also the son of Neha's (only) brother, so Neha's brother is this person's father -- meaning Neha's brother = X = Rita's father.

5. So Neha is Rita's father's sibling -- by the standard naming convention used in these puzzles (Neha is a female name), Neha is Rita's paternal aunt.

Cross-check: “Aunt” does not appear among the four given choices (Niece, Mother-in-law, Sister, Cannot be determined), and none of the other three terms matches a father's-sibling relation either. So even though the family tree pins down the relation precisely, none of the options offered states it correctly -- which is exactly why, among the choices actually given, “Cannot be determined” is the one that fits.

Hence, of the four choices given, the correct pick is “Cannot be determined”.