The correct option is: (A) –5Q
Explanation:
The charge density is Q/area which is Q/4πr2 so for the inner surface it is Qinner/4πa2 and for the outer surface it is Qouter/16πa2. For these to be equal Qouter must be 4Qinner. Because of the +Q charge inside, there is a charge of –Q induced on the inner surface, which means the outer surface must have charge –4Q. Thus the total charge on the shell is –5Q.