Reason : The field just outside the capacitor is $\frac{\sigma }{{{\varepsilon _0}}}$. ( $\sigma $ is the charge density).


$(A)$ the charge on the upper plate of $C _1$ is $2 CV _0$
$(B)$ the charge on the upper plate of $C _1$ is $CV _0$
$(C)$ the charge on the upper plate of $C _2$ is $0$
$(D)$ the charge on the upper plate of $C _2$ is $- CV _0$

