Which is the correct statement?

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:

$A$ metallic solid undergoes Frenkel defect. Its original mass,volume and density are $M_0$,$V_0$ and $D_0$ respectively. After Frenkel defect the mass,volume and density are $M$,$V$ and $D$ respectively. The variations of $M$,$V$ and $D$ after Frenkel defect are

If $10^{-4} \% SrCl_2$ is added to a crystal of $NaCl$,find the number of cationic vacancies created in the crystal.

Which of the following point defects are shown by $AgBr_{(s)}$ crystals?
$A$. Schottky defect
$B$. Frenkel defect
$C$. Metal excess defect
$D$. Metal deficiency defect

In ionic compounds where the sizes of the cation and anion are almost similar,which defect is observed?