What type of crystal defect is indicated in the diagram below? $\mathrm{Na}^{+} \mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-}$ $\mathrm{Cl}^{-} \square \mathrm{Cl}^{-} \square \mathrm{Na}^{+} \square \mathrm{Na}^{+}$ $\mathrm{Na}^{+} \mathrm{Cl}^{-} \square \mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-}$ $\mathrm{Cl}^{-} \mathrm{Na}^{+} \mathrm{Cl}^{-} \mathrm{Na}^{+} \square \mathrm{Na}^{+}$

• A

  Frenkel defect
• B

  Frenkel and Schottky defects
• C

  Interstitial defect
• Correct answer
  D

  Schottky defect

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