The region between two concentric shells of radii a and b $\;(b > a)\;$ contains volume charge density $\;\rho(r)=\large\frac{C}{r}\;$ , where C is a constant and r is the radial distance , as shown in figure . A point charge q is placed at the origin , r=0 . Find the value of C for which the electric field in the region between the spheres is constant.

Question

$(a)\;\large\frac{q}{2 \pi a^2}\qquad(b)\;\large\frac{q}{4 \pi a^2}\qquad(c)\;\large\frac{q}{ \pi a^2}\qquad(d)\;\large\frac{2q}{ \pi a^2}$