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: Understand the defect
A Schottky defect occurs when equal numbers of cations and anions leave their lattice sites, creating vacancies. It is found in ionic solids where the cation and anion are similar in size, such as NaCl and KCl.

Step 2: Check statement (A)
Because ions are missing from the crystal but the volume does not change, mass per unit volume decreases. So the density decreases. (A) is TRUE.

Step 3: Check statement (B)
Equal numbers of positive and negative ions go missing, so the crystal remains electrically neutral. (B) is FALSE.

Step 4: Check statements (C) and (D)
The Schottky defect appears when the cation and anion sizes are nearly equal, not when they differ widely. So (C) is FALSE. Statement (D), a smaller cation moving to an interstitial site, describes a Frenkel defect, so it is FALSE for Schottky.

Final Answer:
Only the statement about decreased density is true. This is option (A). \[ \boxed{\text{(A) }\text{The density of a substance decreases}} \]