A . Impurity defect arises due to replacement of one common ion present in any crystal by another uncommon ion.
B. Metal excess defect is is due to missing of cation from ideal ionic solid which lead to create a F - centre generally occupied by unpaired electrons e.g NaCl with anionic site .
C. metal deficiency defect in FeO , `Fe^(3+)` exists along with ` Fe ^(3+)` which lead to decrease in metal ion (s) so this is a type of metal deficiency defect.
