Q.Assertion : Due to Frenkel defect, density of the crystalline solid decreases. Reason : In Frenkel defect, cation and anion leaves the crystal.

A Frenkel defect only relocates an ion internally (from a regular site to an interstitial site), so no mass leaves the crystal and its density is unaffected — the density decrease and the 'ions leaving the crystal' description in this question both actually describe a Schottky defect, not Frenkel.

Checking the assertion: in a Frenkel defect, a smaller ion (typically the cation, due to its smaller size) leaves its regular lattice site and occupies a nearby interstitial void, while remaining within the crystal. Since no ions actually leave the crystal (mass is conserved, just relocated internally), the overall density of the crystal is unchanged by a Frenkel defect. This is precisely what distinguishes it from a Schottky defect, where equal numbers of cations and anions genuinely leave the crystal, creating vacancies and decreasing the density. So the assertion — that Frenkel defect decreases density — is false.

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