Correct option is D
Given: Six students, F, E, D, C, B and A, were studying around a square table in a college library, facing the centre.
C and E are diagonally opposite. No one sits between C and D or E and F.

A is not at a corner and is a neighbor of E and D.

D is diagonally opposite to F.

B is to the immediate right of F.

Hence Third to the left of B is A.