A family consists of six members P, Q, R, X, Y and Z. Q is the son of R, but R is not the mother of Q. P and R are a married couple. Y is the brother of R. X is the daughter of P. Z is the brother of P. Who is the brother-in-law of R?

Introduction / Context:
This puzzle combines gender clues with marital and sibling relationships. You are told who is married to whom, who is a son or daughter of whom, and which people are brothers. Using this, you must work out who is the brother-in-law of R. Brother-in-law can mean either the brother of one's spouse or the husband of one's sibling, so we must consider both possibilities.

Given Data / Assumptions:
- Family members: P, Q, R, X, Y, Z. - Q is the son of R, but R is not the mother of Q, so R is the father of Q. - P and R are a married couple (so P is R's wife). - Y is the brother of R (Y is male and sibling of R). - X is the daughter of P (child of P and R, female). - Z is the brother of P (male sibling of P).

Concept / Approach:
Once we know that R is male (father of Q) and is married to P, we can search for people who qualify as his brother-in-law. A brother-in-law might be (a) a brother of R's spouse P, or (b) a husband of R's sister. The statements tell us that Z is the brother of P, so Z is a brother of R's wife. That already makes Z a brother-in-law of R. We must also check if Y could qualify via the second definition, but we have no information that Y is married to R's sister, so the safe and supported answer is Z.

Step-by-Step Solution:
Step 1: From Q is the son of R but R is not the mother of Q, we infer that R is male (the father of Q). Step 2: P and R are a married couple, so P is R's spouse. Step 3: X is the daughter of P, and since P is married to R, X is a child of P and R in the next generation. Step 4: Y is the brother of R, so Y is R's male sibling. Step 5: Z is the brother of P, so Z is the male sibling of R's spouse P. Step 6: By definition, the brother of one's spouse is a brother-in-law. Therefore, Z is a brother-in-law of R. Step 7: Y is simply R's own brother, not a brother-in-law, and no information suggests that Y is married to R's sister, so we do not classify Y as R's brother-in-law.

Verification / Alternative check:
Visualise two families connected by marriage: R's parental family includes R and Y as brothers. P's parental family includes P and Z as siblings. When P and R marry, Z becomes R's brother-in-law (through his wife), and Y becomes P's brother-in-law. The network now contains exactly two married people P and R, one child Q (son) and one child X (daughter). All relationships are consistent, and Z is clearly the brother of R's spouse.

Why Other Options Are Wrong:
- P: P is R's wife, not his brother-in-law. - Y: Y is the brother of R, so he is a direct sibling, not an in-law. He could be an in-law to P, but the question is about R. - X: X is the daughter of P and R, belonging to a younger generation, so she cannot be R's brother-in-law. - Q: Q is the son of R, again a younger generation, not an in-law.

Common Pitfalls:
A frequent confusion is to treat any brother in the extended family as a brother-in-law. However, brother-in-law is an in-law relation, not a blood sibling. Another pitfall is forgetting that the spouse's brother qualifies as a brother-in-law. Keeping the two definitions of brother-in-law in mind and matching them against the data leads directly to Z.

Final Answer:
The brother-in-law of R is Z.