Step-by-step explanation:
Formula for the capacitance of a parallel plate capacitor is as follows.
C =

where, A = area = 1
=

d = diameter = 1 mm =

Hence, putting the given values into the above formula as follows.
C =

=

=

Now, we will calculate the energy stored in the capacitor as follows.
U =

=

=

or, =
Thus, we can conclude that energy stored on each capacitor is
.