The charge on the electron is 1.6x10^-19C. So, 10^24 of them will be a charge of 1.6x10^5C, F = q1xq2/[(4pi epsilon nought)r^2]
(a) The capacitance of the capacitor is:

and the voltage applied across its plates is

The relationship between the charge Q on each plate of the capacitor, the capacitance and the voltage is:

and re-arranging it we find the charge stored in the capacitor:

(b) The electrical potential energy stored in a capacitor is given by

where C is the capacitance and V is the voltage. The new voltage is

so the energy stored in the capacitor is
Answer:
Option (b)
Explanation:
let the weight of boat is W. In equilibrium condition, the weight of boat is equal to the buoyant force acting on the boat.
The buoyant force acting on the boat is equal to the weight of water displaced by the boat.
In case of fresh water:
Weight of the boat = weight of fresh water displaced by the boat
W = Volume of fresh water displaced x density of fresh water x g
W = V x 1 x g
W = V x g ....... (1)
In case of salt water:
Let the volume of salt water displaced is V'.
Weight of the boat = weight of salt water displaced by the boat
W = Volume of salt water displaced x density of salt water x g
W = V' x 1.02 x g ..... (2)
Equate equation (1) and equation (2), we get
V x g = V' x 1.02 x g
V' = 0.98 V
Thus, option (b) is true.