Define the compressibility factor $(Z)$ in terms of the molar volume of a gas.

• A
  $Z = \frac{V_{m, real}}{V_{m, ideal}}$
• B
  $Z = \frac{V_{m, ideal}}{V_{m, real}}$
• C
  $Z = V_{m, real} \times V_{m, ideal}$
• D
  $Z = V_{m, real} + V_{m, ideal}$