No current flows
Hence \(Q_{A}=C V\)
For \((\mathrm{B})\)
\(\mathrm{i}=\frac{\mathrm{V}}{\mathrm{R}} \mathrm{e}^{-\frac{\mathrm{t}}{\mathrm{RC}}}\)
\(\mathrm{q}=\mathrm{CV} \mathrm{e}^{\frac{\mathrm{t}}{\mathrm{RC}}}\)
at \(\mathrm{t}=\mathrm{CR}\)
\(\mathrm{Q}_{\mathrm{B}}=\mathrm{CV} \mathrm{e}^{-1}=\frac{\mathrm{CV}}{\mathrm{e}}\)