$A$ charge of total amount $Q$ is distributed over two concentric hollow spheres of radii $r$ and $R$ $(R > r)$ such that the surface charge densities on the two spheres are equal. The electric potential at the common centre is

  • A
    $\frac{1}{4\pi \varepsilon_0} \frac{(R - r)Q}{(R^2 + r^2)}$
  • B
    $\frac{1}{4\pi \varepsilon_0} \frac{(R + r)Q}{2(R^3 + r^3)}$
  • C
    $\frac{1}{4\pi \varepsilon_0} \frac{(R + r)Q}{(R^2 + r^2)}$
  • D
    $\frac{1}{4\pi \varepsilon_0} \frac{(R - r)Q}{2(R^2 + r^2)}$

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