The compressibility factor of a gas is given by (where, V1 = actual volume of the gas V2 = gas volume predicted by ideal gas law)

Answer: Option A

The compressibility factor is given by $$Z=\frac{P{V}_1}{RT}.$$   If at the same temperature and pressure if the same gas exists as ideal gas than we can write:
$$\begin{array}{l}Z=1=\frac{P{V}_2}{RT}\Rightarrow \frac{RT}{P}=V_2\\ \mathrm{So},Z=\frac{V_1}{V_2}.\end{array}$$