When $CaC{l}_2$ is added to $AgCl$ crystal, the defect introduced is

When mixing $AgCl$ and $CaC{l}_2$, each added ion of $C{a}^{2+}$ replaces $A{g}^{+}$ as they have similar radii. Since, the charge of $Ca$ and $Ag$ is of $+2$ and $+1$ $+1$ respectively, it leads to the formation of positive vacancies (schottky defect) It means that one mole of $CaC{l}_2$ provides one mole of $Ag$ vacancies in crystal structure.