Explanation:

- Raj says, "His mother is the wife of my father’s son."

- "My father's son" refers to Raj himself, as he has no brothers.

- So, "the wife of my father’s son" is Raj's wife.

- Thus, "his mother" is Raj's wife, meaning the boy is Raj's son.

- Raj also mentions, "Brothers and sisters I have none," confirming he is his father's only son.

- Let's look at the options:

- Option 1: His son - This is consistent with the statements.

- Option 2: His cousin - Would require siblings.

- Option 3: His uncle - Implies older generation.

- Option 4: His nephew - Implies a sibling.

Therefore, the correct answer is:

- Option 1: His son