A crystal of KCl containing $\mathrm{CaCl}_2$ as an impurity has a lower density than that of pure KCl , because it has

• A

  vacant $\mathrm{Cl}^{-}$sites.
• Correct answer
  B

  vacant $\mathrm{K}^{+}$sites.
• C

  $\mathrm{K}^{+}$ions in the interstitial sites.
• D

  $\mathrm{Cl}^{-}$ions in the interstitial sites.

Hence, the correct answer is option: 'B'.