If the electric potential of the inner metal sphere is 10 volt & that of the outer shell is 5 volt, then the potential at the centre will be :

Electric potential in the hollow sphere is constant and equal to that on the surface. [If no charged body is present inside sphere]

$\Rightarrow$${\mathrm{V}}_{\mathrm{c}}=10 \mathrm{V} \left[\because \mathrm{centre} \mathrm{is} \mathrm{inside} \mathrm{the} \mathrm{inner} \mathrm{sphere}\right]$