JEE Main 2022 · 28 June · morning · Single correct · +4 / −1
The incorrect statement about the imperfections in solids is :
- (a) Schottky defect decreases the density of the substance.
- (b) Interstitial defect increases the density of the substance.
- (c) Frenkel defect does not alter the density of the substance.
- (d) Vacancy defect increases the density of the substance.
Answer and solution
Answer (d) Vacancy defect increases the density of the substance.
Solution
Chemistry ma’am · 2 steps
Density is mass over the same volume, so just ask whether the defect removes atoms or adds them.
- Density test. The lattice volume barely changes with a point defect. So density falls if atoms go missing, rises if extra atoms squeeze in, and stays the same if atoms only move.
Defect What happens to atoms Density Statement Schottky Equal numbers of cations and anions leave the crystal decreases (a) correct Interstitial Extra atoms occupy gaps between lattice sites increases (b) correct Frenkel An ion shifts from its site to an interstitial site, nothing leaves unchanged (c) correct Vacancy Some lattice sites are left empty decreases (d) incorrect - So. A vacancy means missing atoms in the same volume, so density goes down, not up. The incorrect statement is (d).
The idea to keep. Missing atoms lower density (vacancy, Schottky). Extra atoms raise it (interstitial). Atoms that only move keep it the same (Frenkel).
Answer from the NTA final answer key. Solution by PrepWiser.