b.(5%) Why Divergence of Curl of a vector field is zero, that is, ∇. ( ∇ X A) =0?

(5%) A point charge Q exists at (0, d, 0) in space, as shown in Figure (a). Using Theory of image, a point charge of -Q exists at (0, -d, 0) symmetrically, as indicated in Figure (b). The dielectric constant of the space is εo. Write the electric intensities (Ex|y=0, Ey|y=0, and Ez|y=0) for a point on the ZX-plane in terms of (d and R), or (d and r), as indicated in Figure (b).