Electron-deficient impurities are caused by the elements of which group?

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 ionic crystals exhibits Frenkel defect?

If $NaCl$ is doped with $10^{-3} \, mol \%$ of $SrCl_{2}$,what is the concentration of cation vacancies?

Identify the type of defect from the following in stainless steel.

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