Question

Which of the following point defects are shown by AgBr crystals? I. Metal excess defect, II. Schottky defect, III. Metal deficiency defect, IV. Frenkel defect

• A. I & II
• B. II & IV
• C. I, II & III
• D. I & IV

Hint:

AgBr is the "dual-defect" crystal—it shows both Frenkel and Schottky defects!

Answer 1

The Correct Option is B

Step 1: Recall the common point defects.
Schottky defect: equal numbers of cations and anions go missing. Frenkel defect: a small ion slips from its site into an interstitial gap. Metal excess and metal deficiency are non-stoichiometric defects.

Step 2: Look at AgBr.
Silver bromide is a special case because it shows two intrinsic defects at the same time.

Step 3: Why Frenkel (IV) appears.
The $Ag^+$ ion is small, so it easily leaves its lattice point and squeezes into an interstitial site. This gives a Frenkel defect.

Step 4: Why Schottky (II) appears.
AgBr also loses pairs of $Ag^+$ and $Br^-$ ions together, which is the Schottky defect.

Step 5: Rule out the others.
Metal excess (I) and metal deficiency (III) are non-stoichiometric defects, not shown by pure AgBr.

Step 6: Conclusion.
So AgBr shows Schottky and Frenkel defects, that is II and IV. \[ \boxed{\text{II and IV}} \]