Question : How is the girl in the photograph related to Kunal?

Statements :
I. Pointing to the photograph, Kunal said, "She is the mother of my father's only granddaughter".
II. Kunal has no siblings.
III. Pointing to the photograph, Kunal said, "She is the only daughter-in-law of my mother."

Explanation:-

From I, we conclude that the girl is either Kunal's or his brother's wife. But, according to II, Kunal has no siblings.
So, from both I and II, we conclude that the girl is Kunal's wife.
From III, we find that the girl is the only daughter-in-law of Kunal's mother i.e. she is Kunal's wife.