What is the similarity between solid solutions of
I. SrCl₂ and NaCl ?
II.CdCl₂ and AgCl ?

Both the solutions show impurity defect. When molten NaCl containing a little amount of SrCl₂ is crystallised, some of the sites of Na⁺ ions are occupied by Sr²⁺. Each Sr²⁺ replaces two Na*ions. It occupies the site of only one ion and the other site remains vacant. The cationic vacancies, hence produced are same in number as that of Sr²⁺ ions. Same case is with the solid solution of CdCl₂ and AgCl.