Ncert Exercises & Solutions

Match the types of defects given in Column I with the statement given in Column II.

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

Codes

	A	B	C
1.	2	3	1
2.	3	1	2
3	1	2	3
4.	2	1	3

Hint: Non-Stoichiometric Defects.

Explanation:

A. Impurity defect arises due to replacement of one common ion present in any crystal by another uncommon ion. In the case of NaCl, some of the sites of Na⁺ ions are occupied by Sr²⁺ 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., NaCl with the anionic site.

C. Metal deficiency defect In FeO, Fe³⁺ exists along with Fe²⁺ which lead to a decrease in metal ion(s) so this is a type of metal deficiency defect.

Thus, option 2 is the correct answer.

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