Which one of the following has Frenkel defect?

Which relationship is correct regarding the coordination number and the size of cations and anions in ionic compounds exhibiting Schottky defect?

Select the incorrect statement.

Explain the following term with a suitable example:
$(i)$ Schottky defect

Which among the following statements is true about Schottky defect?

The pyknometric density of sodium chloride crystal is $2.165 \times 10^3 \ kg \ m^{-3}$ while its $X$-ray density is $2.178 \times 10^3 \ kg \ m^{-3}$. The fraction of unoccupied sites in sodium chloride crystal is