Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

Explanation

Let us take an example NaCl doped with SrCl, impurity when SrCl2 is added to NaCl solid as an impuriyt, two `Na^(+)` ions will be replaced and one of their sites will be occupied by Sr 21-whilte the other will remain vacant. Thus, we can say that when a cation of higher valence is added as an impurity to an ionic solid, two or more cations of lower valency are replaced by a cation of higehr valency to maintain electrical neutrality Hence, some cationic vacancies are created.