A

To determine the magnetic field around the square loop PQRS where current enters at P and exits at S, we apply Ampère's Circuital Law and the right-hand rule.
Step 1: Identify the direction of current flow. The current enters at P, travels through PQ, QR, RS, and exits at S.
Step 2: Using the right-hand rule (thumb points in the direction of current and fingers curl in the direction of the magnetic field), we find that inside the square loop, the magnetic field lines are directed outwards.
Step 3: The contributions to the magnetic field at the center of the loop from all segments of wire combine constructively, leading to a maximum magnetic field at that point.
Conclusion: Thus, the magnetic field is maximum at the center of the loop. Therefore, the correct answer is option A.