Which among the following solids shows Frenkel defect?

Which of the following is not a function of an impurity present in a crystal?

$NaCl$ is doped with $2 \times 10^{-3} \, mol \% \, SrCl_2$. What is the concentration of cation vacancies?

Potassium crystallizes in an $FCC$ lattice with a unit cell edge length of $0.5 \ nm$. The approximate density (in $g \ cm^{-3}$), if it contains $0.1 \%$ Schottky defects, is:

Which of the following is an incorrect statement?

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 .....