In the electric circuit given below, capacitance of each capacitor is $1$ $\mu F$. the effective capacitance between the points $A$ and $B$ is- ( in $\mu F$)

When a potential difference of ${10}^3 \mathrm{V}$ is applied between $\mathrm{A}$ and $\mathrm{B}\text{,}$ a charge of $0.75 \mathrm{mC}$ is stored in the system of capacitors. The value of $C$ is $\left(\mathrm{\mu F}\right)$

What is effective capacitance between points $X$ and $Y$ in fig.-

The capacitors $A$ and $B$ are connected in series with a battery as shown in the figure. When the switch $S$ is closed and the two capacitors get charged fully, then