Block is moving in the circular path, that means there should be a force which is keeping the block in contact with the wall here that force is normal force, which is towards the center of the circular path. And we know this force is equal to ${{m{v^2}} \over r}$.

$$ \therefore $$ $$N = {{m{v^2}} \over r}$$

$$ \Rightarrow $$ N $$ \propto $$ v²

$$\Rightarrow$$ The graph given in option A suits the best for the above relation.