Who is the doctor ?

• Q is the brother of P and is neither a doctor nor an artist, so Q must be the lawyer.

• P and S are unmarried students, which implies they are not the married individuals or the primary professionals identified in the other constraints, but more importantly, we look at the remaining roles.

• R is explicitly stated to be not a doctor.

• Since Q is the lawyer and R is not the doctor, the doctor must be either P, S, or T.

• P and S are students, and typically in such logical puzzles, 'student' is a distinct status from the professional roles (doctor, lawyer, artist) unless specified otherwise, but let's look at T.

• T is a man married to one of the group members. The group has one doctor, one lawyer, and one artist. Q is the lawyer. R is not the doctor. If P or S were the doctor, they would be students who are doctors, which is possible, but let's re-evaluate the 'student' constraint. Usually, 'student' excludes being a practicing professional like a doctor or lawyer in these specific UPSC logic sets unless it's a medical student. However, the key constraint is: Q is Lawyer. R is not Doctor. P and S are students. T is the only one left who fits the profile of a professional (Doctor or Artist) without being excluded by the 'student' or 'not doctor' tags directly in a way that forces the other. Let's look closer: Q=Lawyer. R != Doctor. P, S = Students. T = Married Man. The roles are Doctor, Lawyer, Artist. Q is Lawyer. Who is Doctor? R is not. P and S are students (often implying they don't hold the professional title yet, or are distinct from the 'professional' set). T is the only adult professional candidate left for Doctor or Artist. If T were the Artist, who would be the Doctor? P, S, or R. R is not. P and S are students. In many such problems, 'Student' is a distractor for the professional role, or implies they are not the Doctor. Let's assume the standard interpretation: Q is Lawyer. R is not Doctor. P and S are students (thus not the Doctor/Lawyer/Artist professionals in the active sense, or simply that T is the only one left to be the Doctor if P/S are excluded by the 'student' tag from being the 'Doctor' in the context of the group's professional identities). Actually, a simpler deduction: Q is Lawyer. R is not Doctor. P and S are students. T is the only one who can be the Doctor because P and S are students (and thus not the practicing doctor in this context) and R is explicitly not the doctor. Therefore, T is the doctor.