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

Schottky defect is generally observed in which of the following?

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

Calcium crystallizes in a face-centred cubic $(FCC)$ lattice with an edge length of $556 \ pm$. Calculate the density if:
$(i)$ There is $0.1 \%$ Schottky defect.
$(ii)$ There is $0.1 \%$ Frenkel defect.

$A$ solid solution of $CdCl_2$ and $AgCl$ exhibits which type of defect?

An element $X$ (atomic weight = $24$) crystallises in a face-centered cubic $(FCC)$ lattice. The edge length of the unit cell is $400 \, pm$. If this lattice contains $4\%$ Schottky defects,calculate the observed density of this element in $g/cm^3$ $(N_A = 6 \times 10^{23})$.