Question

Which of the following statements is true about schottky defect ?

• A. The density of a substance decreases.
• B. The electrical neutrality of the substance changes.
• C. It is found in ionic compounds with larger difference between sizes of cation and anion.
• D. It develops when smaller cations occupy interstial sites from their normal sites.

Hint:

In Schottky defect equal numbers of cations and anions are missing, so mass drops while volume stays the same.

Answer 1

The Correct Option is A

Step 1: Picture
Imagine removing a pair of ions, one Na+ and one Cl-, from the crystal of NaCl. The lattice keeps its size but now has two empty sites.

Step 2: Effect on density
Fewer ions in the same volume means lower mass per unit volume, so the density decreases. This agrees with statement (A).

Step 3: Other statements
Charge balance is kept because ions are removed in equal numbers, so (B) is not correct. The defect is favoured when the ions are similar in size, so (C) is not correct. Moving an ion to an interstitial site is a Frenkel defect, so (D) is not correct.

Step 4: Answer
Option (A) is the only true statement.

Final Answer:
Density falls in a Schottky defect. This is option (A). \[ \boxed{\text{(A) }\text{The density of a substance decreases}} \]