Question

Schottky defects occurs mainly in electrovalent compounds where

• A. positive ions and negative ions are of different size
• B. positive ions and negative ions are of same size
• C. positive ions are small and negative ions are big
• D. positive ions are big and negative ions are small

Hint:

Schottky defect: equal number of cations and anions missing, common in ionic solids with similar sized ions.

Answer 1

The Correct Option is B

Step 1: Define Schottky defect.
Schottky defect is a type of point defect in ionic crystals where equal number of cations and anions are missing from their lattice sites.
Step 2: Condition for Schottky defect.
This defect is mainly found when both ions are of comparable sizes, so that removing them does not distort the lattice much.
Examples: NaCl, KCl, CsCl.
Step 3: Conclusion.
Thus Schottky defect occurs mainly when positive and negative ions are of same size.
Final Answer:
\[ \boxed{\text{(B) positive ions and negative ions are of same size}} \]