Four identical condensers are connected in parallel and then in series. The ratio of equivalent capacitance in series to that in parallel combination is

The correct option is (D).
Concept: The potential drop across condensers in parallel is the same. The net potential drop across condensers in series should add up and the charge on each plate of condensers is the same in series.
Suppose Q charge is on each condenser. For identical condensers of each capacitance \(\mathrm{C}\) in parallel combination: \(V=\frac{\mathrm{Q}}{\mathrm{C}}=\frac{4 \mathrm{Q}}{\mathrm{C}_{\|}}\)
So, \(\mathrm{C}_{\|}=4 \mathrm{C}\)
Suppose Q charge is on each condenser, then the net potential drop across the circuit with resistors in series is,
\(\mathrm{V}=\frac{\mathrm{Q}}{\mathrm{C}_{\mathrm{S}}}=\frac{\mathrm{Q}}{\mathrm{C}}+\frac{\mathrm{Q}}{\mathrm{C}}+\frac{\mathrm{Q}}{\mathrm{C}}+\frac{\mathrm{Q}}{\mathrm{C}}\).
So, \(\mathrm{C}_{\mathrm{s}}=\frac{\mathrm{c}}{4}\).
The ratio of equivalent capacitance in series to that in parallel combination is \(\frac{\mathrm{C}_{\mathrm{s}}}{\mathrm{C}_{\|}}=\frac{\mathrm{C}}{4} \times \frac{1}{4 \mathrm{C}}=\frac{1}{16}\)