What kind of defects do most ionic crystals possess?

If $10^{-4} \, \text{mole} \%$ of $SrCl_2$ is added to $NaCl$,the concentration of cation vacancies created is...... $(N_A = 6.02 \times 10^{23} \, \text{mol}^{-1})$

Ionic solids,which have anionic vacancies due to metal excess defect,develop colour. Explain with the help of a suitable example.

What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?

Which type of defect is observed in crystals like $NaCl$ and $KCl$?

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