Three concentric metal shells A, B and C of respective radii a, b and c (a < b < c) have surface charge densities $+\sigma, \; -\sigma$ and $+\sigma$ respectively. The potential of shell B is :

Question

( A ) $\frac{\sigma}{\varepsilon_0} [ \frac{a^2 - b^2}{a} + c]$
( B ) $\frac{\sigma}{\varepsilon_0} [ \frac{a^2 - b^2}{b} + c]$
( C ) $\frac{\sigma}{\varepsilon_0} [ \frac{b^2 - c^2}{c} + a]$
( D ) $\frac{\sigma}{\varepsilon_0} [ \frac{b^2 - c^2}{b} + a]$