P, Q, R, S, T and U are six members of a family. R is the spouse of Q, U is the mother of T and S is the daughter of U. P's daughter is T and R's son is P. There are two couples in the family. Which one of the following is correct?

P, Q, R, S, T and U are six members of a family. R is the spouse of Q,…

Answer

Given relations: R is spouse of Q. R's son is P, so P is child of R and Q. P's daughter is T, so T is child of P. U is mother of T and S is daughter of U, so U is spouse of P and the two couples are R-Q and P-U.
Key inference: Since P's daughter is T, T is female. Also, T is the child of P, and P is the child of Q-R; therefore T is the grandchild of Q.
(a) Q is the grandfather of T — Not निश्चित. Q's gender is not fixed because only R's gender can be inferred from option testing, not Q's directly from the statements.
(b) Q is the grandmother of T — Not निश्चित. Same reason: Q could be male or female from the given statements alone.
(c) R is the mother of P — Not definite. R is only known to be spouse of Q and parent of P; father/mother cannot be fixed from the statements.
(d) T is the granddaughter of Q — Correct. T is explicitly a daughter of P, hence female, and she is a grandchild of Q; therefore she is granddaughter of Q.
Correction: My earlier error was treating Q's gender as fixed. The statements fix T's gender, not Q's. Hence the safe and correct conclusion is (d).