Pointing to a boy, a man said, “He is the son of the only daughter of my mother.” How is the boy related to the man?

The correct option is Nephew.

To determine how the boy is related to the man, we can break down the statement step-by-step from the perspective of the man speaking:

1. “my mother”: This refers to the man's mother.

2. “the only daughter of my mother”: Since the man's mother has only one daughter, that daughter must be the man's sister (assuming the man is male).

3. “He is the son of [the only daughter of my mother]”: Replacing the phrase with our previous deduction, the boy is the son of the man's sister.

The son of one's sister is their nephew.

Therefore, the boy is the man's nephew.