Two identical charged spherical drops,each at a potential $V$,coalesce to form a single larger drop. If the capacitance of each small drop is $C$,find the potential of the larger drop.

$A$ positive point charge of $10^{-8} \ C$ is kept at a distance of $20 \ cm$ from the center of a neutral conducting sphere of radius $10 \ cm$. The sphere is then grounded and the charge on the sphere is measured. The grounding is then removed and subsequently the point charge is moved by a distance of $10 \ cm$ further away from the center of the sphere along the radial direction. Taking $\frac{1}{4 \pi \epsilon_0} = 9 \times 10^9 \ N \cdot m^2 / C^2$ (where $\epsilon_0$ is the permittivity of free space),which of the following statements is/are correct:
$(A)$ Before the grounding,the electrostatic potential of the sphere is $450 \ V$.
$(B)$ Charge flowing from the sphere to the ground because of grounding is $5 \times 10^{-9} \ C$.
$(C)$ After the grounding is removed,the charge on the sphere is $-5 \times 10^{-9} \ C$.
$(D)$ The final electrostatic potential of the sphere is $300 \ V$.

$A$ $4\,\mu F$ capacitor is connected in parallel to another capacitor of $8\,\mu F$. Both the capacitors are then connected in series with a $12\,\mu F$ capacitor and charged to $20\;V$. The charge on the plate of the $4\,\mu F$ capacitor is......$\mu C$.

See the diagram. The area of each plate is $2.0 \,m^{2}$ and $d=2 \times 10^{-3} \,m$. $A$ charge of $8.85 \times 10^{-8} \,C$ is given to plate $Q$. Then the potential of $Q$ becomes (in $\,V$)

If a capacitor of capacitance $100 \mu F$ is charged at a steady rate of $100 \mu C s^{-1}$,then the time taken to produce a potential difference of $100 \ V$ between the capacitor plates is (in $s$)

For a hollow spherical shell of radius $R$ carrying a charge $q$,how does the electric potential $(V)$ change with respect to the distance $(s)$ from the centre?