What is the answer to Q.No 15?

Charge induced by +Q and -Q on the inner surface is -Q and +Q respectively.
so, net charge induced is Zero. But the surface charge density is not zero inside. Region near to +Q is negatively charge induced and reverse for -Q. So, surface charge density is uneven and non-zero.
But outside surface charge is simply zero from Gauss’ Law and so, no surface charge.
Option 3