The molar conductivity of $0.01 \ M$ acetic acid at $25^{\circ} C$ is $16.5 \ \Omega^{-1} \ cm^2 \ mol^{-1}$ and its molar conductivity at infinite dilution is $390.7 \ \Omega^{-1} \ cm^2 \ mol^{-1}$. What is its degree of dissociation?

• A
  $0.0223$
• B
  $0.0422$
• C
  $0.0642$
• D
  $0.0821$