A hollow conducting sphere of inner radius R and outer radius 2R is given charge Q as shown in the figure, then the

Points ,A and B lie within the same metal hence ${\mathrm{V}}_{\mathrm{A}}={\mathrm{V}}_{\mathrm{B}}$. The potential inside a hollow sphere is same as potential at the surface, hence ${\mathrm{V}}_{\mathrm{A}}={\mathrm{V}}_B={\mathrm{V}}_{\mathrm{C}}={\mathrm{V}}_O$.