As plates are moved far away further, capacity of capacitor $\left(C=\frac{\varepsilon_0 A}{d}\right)$ decreases.
As battery remains connected during this activity, potential difference between plates remains same.
So, the charge on plates $(Q=C V)$ decreases.
Also, energy of capacitor $\left(U=\frac{1}{2} C V^2\right)$ decreases as capacitance decreases. So, correct option is $( d )$.


| Capacitor | Capacitance |
| $(A)$ Cylindrical capacitor | $(i)$ ${4\pi { \in _0}R}$ |
| $(B)$ Spherical capacitor | $(ii)$ $\frac{{KA{ \in _0}}}{d}$ |
| $(C)$ Parallel plate capacitor having dielectric between its plates | $(iii)$ $\frac{{2\pi{ \in _0}\ell }}{{ln\left( {{r_2}/{r_1}} \right)}}$ |
| $(D)$ Isolated spherical conductor | $(iv)$ $\frac{{4\pi { \in _0}{r_1}{r_2}}}{{{r_2} - {r_1}}}$ |


Reason : $\frac{1}{{{C_p}}} = \frac{1}{{{C_1}}} + \frac{1}{{{C_2}}} + \frac{1}{{{C_3}}}$