Consider a spherical surface of radius 4m centred at the origin . Point +q and -2q are fixed at points $\;A (2m , 0 , 0)\;$ and $\;B (8m , 0 ,0)\;$ respectively . The potential on the surface of sphere is

Question

$(a)\;\large\frac{k\;q}{2}\qquad(b)\;-\large\frac{2\;k\;q}{4}\qquad(c)\;-\large\frac{k\;q}{2}\qquad(d)\;zero$