A charge Q is distributed over two concentric conducting thin spherical shells radii r and R (R > r). If the surface charge densities on the two shells are equal, the electric potential at the common centre is:

A

$$\frac{1}{4\pi\epsilon_0}\frac{(R+r)}{2(R^2+r^2)}Q$$

B

$$\frac{1}{4\pi\epsilon_0}\frac{(2R+r)}{(R^2+r^2)}Q$$

C

$$\frac{1}{4\pi\epsilon_0}\frac{(R+2r)Q}{2(R^2+r^2)}$$

D

$$\frac{1}{4\pi\epsilon_0}\frac{(R+r)}{(R^2+r^2)}Q$$