question_answer 116)

    Match the types of defect given in Column I with the statement given in

	Column I	Column II
A.   B. C.	Impurity defect Metal excess defect Metal deficiency defect	1. NaCl with anionic sites called F-centres 2. Fed with Fe3+ 3. NaCI with Sr2+ and some cationic sites vacant

Answer:

                    A.® (3)    B.® (1)   C.® (2) A. Impurity defect arises due to replacement of one common ion present in any crystal by another uncommon ion. B. Metal excess defect is due to missing of cation from ideal ionic solid which lead to create a F-centre generally occupied by unpaired electrons, e.g., NaCI with anionic site. C. Metal deficiency defect In FeO, Fe3'1' exists along with Fe2''' which lead to decrease in metal ion(s) so this is a type of metal deficiency defect.