Two metal plates of area 'A' from a parallel plate capacitor with air in between the plates. The distance between the plate is 'd'. A metal plate of thickness $\large\frac{d}{2}$ and of the same area A is inserted between the plates to from two capacitors of capacitance $C_1$ and $C_2$ as shown in the figure. If the effective capacitance of the two capacitor is $C'$ and the capacitance of the capacitor initially is $C$, then $\large\frac{C'}{C}$ is

Question

(a) 4 (b) 2 (c) 6 (d) 1