A parallel plate capacitor filled with oil of dielectric constant $k = 3$, has a capacitance c. After removing the oil between the plates, the capacitance of the capacitor will become

$\frac{1}{3} C$

The correct answer is Option (4) → $\frac{1}{3} C$

Capacitance with dielectric: $C = k C_0$, where $C_0$ is capacitance without dielectric

Given: $k = 3$, $C = k C_0 = 3 C_0 \;\Rightarrow\; C_0 = \frac{C}{3}$

Capacitance without dielectric = $C/3$