During the extraction of sodium metal by electrolysis,a mixture of $40\% \ NaCl$ and $60\% \ CaCl_2$ is used because...

• A
  It helps in conducting electricity.
• B
  The melting point of this mixture is lower than the melting point of $NaCl$.
• C
  $Ca^{2+}$ ions displace $Na^+$ ions.
• D
  $Ca^{2+}$ ions reduce to $Na$.