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

• A
  it helps in the conduction of electricity
• B
  the melting point of this mixture is lower than the melting point of $NaCl$
• C
  $Ca^{2+}$ ions from $CaCl_2$ displace $Na^+$ ions from $NaCl$
• D
  $Ca^{2+}$ ions can reduce $NaCl$ to $Na$