In decipher jumbled up description type of questions, a round-about description is given in the form of certain small relationships and direct relationship between the persons concerned is to be deciphered.
Looking at a portrait of a man, Harsh said, "His mother is the wife of my father's son. Brothers and sisters I have none." At whose portrait was Harsh looking ?
Since Harsh has no brother or sister, so he is his father's only son.
Now, wife of my father's son -- my wife.
So, Harsh's wife is the man's mother or the man is Harsh's son.