Introducing Rita to the guests, Neeraj said, "Her sister's father is…

The correct answer is Option (1) → Brother

The statement has two parts; each is turned into a relation of Rita or of Neeraj, and the two are then joined.

• “Her sister’s father”:

  • Sisters have the same father

  • So Rita’s sister’s father is Rita’s father

• “The only son of my grandmother”:

  • Neeraj’s grandmother (his father’s mother) has only one son

  • So that son is Neeraj’s father

• Joining the two:

  • Rita’s father is Neeraj’s father

  • So Neeraj and Rita are children of the same father, and Neeraj is Rita’s brother

Note: “My grandmother” is read here as Neeraj’s father’s mother, the usual reading in such questions. If she were his mother’s mother, her only son would be Neeraj’s maternal uncle, and Neeraj would be Rita’s cousin (Option 4).