P has a son and a daughter. S is the mother of T. S is R's spouse. Q and R are children of P. Then how is Q related to S?

The correct answer is D) Q is a sister of the husband of S.

Step-by-Step Logical Deduction:

1. Identify P's children: The premise states that P has exactly one son and one daughter. We are also told that Q and R are the children of P.
2. Determine genders through marriage: We know that S is the mother of T, which establishes that S is female. The problem states that S is R's spouse. Since S is a female (wife), her spouse R must be logically identified as male (husband).
3. Assign genders to Q and R: Because R is male, he is the son of P. Since P has exactly one son and one daughter, and R is the son, Q must inherently be the daughter of P. Thus, Q is female and is the sister of R.
4. Establish the final relationship: S is married to R (S is the wife, R is the husband). Q is the sister of R. Therefore, Q is the sister of S's husband.

Why the other options are incorrect:

• A) Q is a sister of S: Incorrect. Q and S do not share parents; Q is the sister of R (S's husband), making them sisters-in-law.
• B) Q is a daughter of S: Incorrect. Q is from the same generation as S and R; Q is the daughter of P, not the daughter of S.
• C) Q is the mother of S: Incorrect. Q is in the same generation as S, and S's parentage is not defined in the premises.

Concluding Takeaway: When tackling Blood Relation puzzles in the UPSC Civil Services Aptitude Test (CSAT Paper II, a component introduced in 2011 to evaluate logical reasoning and analytical ability), quickly sketch a family tree using standard demographic symbols (e.g., squares for males, circles for females). Always deduce the gender of unspecified individuals by examining their spouse or sibling constraints!