Question

what is impurity defects....?

Answer 1

this is the impurity defect

Answer 2

ln case if a molten NaCI which contains a little amount of SrCl2 is crystallised, then there we will see that some of the sites of Na+ ions are getting occupied by Sr.

It means that Each Sr is replaced by two Na+ lons. It occupies such that the site of one ion & the rest of the other site remains vacant.

But the cationic vacancies thus which are produced are equal in number as that of Sr²+ ions. There is another example as like this case in the solid solution of CdCl2 & AgCl.