will exert a force on the ring if the ring

A) carries a current

B) has uniform charge distribution

C) has non-uniform charge distribution

D)none of the above.

is the answer (C)???

The answer has to be D.

A - Not possible as the formula for magnetic force is i dlxB = i dl.B.sin@.

Now if the ring carries current, the current and magnetic field of wire on the ring are parellel at every point(direction tangential to the ring). Means sin@=0, means net force=0.

B,C- Not possible as the formula for magnetic force is q vxB = qvbsin@. Now even if the ring is charged but if its stationary, means v=0, then again net force=0.

Hence D is the only option left and its the answer.

Hope U get it.