Topic: Ionic bonding and lattice enthalpy· Chemical Bonding and Molecular Structure

Which is the incorrect statement ?

1. Density decreases in case of crystals with Schottky's defect.

2. NaCl(s) is insulator, silicon is semiconductor, silver is conductor, quartz is piezo electric crystal.

3. Frenkel defect is favoured in those ionic compounds in which sizes of cation and anions are almost equal.

4. \(FeO_{0.98}\) has non stoichiometric metal deficiency defect.

Doubtly Asked 30 Oct 2026 NEET UG 2017 neet Save WhatsApp Report

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Answer: 3. Frenkel defect is favoured in those ionic compounds in which sizes of cation and anions are almost equal.

Key idea: Frenkel defect needs a small cation that can fit into interstitial spaces.

It occurs in compounds where the cation is much smaller than the anion (e.g. AgBr, ZnS), not when sizes are nearly equal. So statement 3 is incorrect. Statement 1 is true (Schottky defect lowers density), 2 is true, and 4 is true (\(\mathrm{FeO_{0.98}}\) has metal deficiency).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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Which is the incorrect statement ?

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