We need more information. Is there a charge on the ring? Perhaps a verb would be useful too.

Ring has +ive charge .

Consider the ring as a set of equidistant point charges and remember the superposition proiciple and that potential is a scalar. A semicircular ring is nothing else but a lot of point charges q arranged in a certain geometry around the center. You know what the potential of a point charge is. It is proportional to q/R. Each of those imaginary point charges makes the same contribution into the total potential at the center, because they all are the same distance R away from the center. Sum over all charges.

Help me . Make of this problem.

I .want ans in form of derivation .with explanation