Answer:
Explanation:
(1.a)
Write the expression for old parallel plate capacitor.

The expression of energy stored in the capacitor without any dielectric between the plate is:

Substitute
for C

Supply source is same therefore, the potential difference is constant. So, the energy stored is:

Write the expression for new parallel plate capacitor.

Substitute
for C' in expression 

From equation (1) and (2).

The ratio of energy stored after the dielectric is introduced to the energy stored in the empty capacitor is 
(1.b)
Write the expression for the capacitor
.

The expression for the energy stored by the capacitor is:

Substitute
for C.

When the distance between the plates is increased and the potential difference between the plates remains constant, then energy stored by the capacitor decreases. Similarly, if the distance between the plates decreases and potential remains constant, then energy stored by the capacitor is increased.
(1.c)
Write the expression for the original charge.

After inserting the dielectric k , the new charge:

From equation (3) and (4).

The charge on the capacitor increases by k