Frenkel defect is generally observed in which of the following?

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

Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

Explain the metal excess defect.

Analysis of the density of an electrically neutral $NaCl$ crystal containing vacancies yielded the following results:
$(i)$ Density of $NaCl$ crystal with all sites occupied $= 2.178 \times 10^3 \ kg \ m^{-3}$
$(ii)$ Density of $NaCl$ crystal with vacancies $= 2.165 \times 10^3 \ kg \ m^{-3}$
Then the percentage of vacancies in the $NaCl$ crystal is .....

Due to vacancy defects,the density of a solid substance .............