Q28 / 90 · JEE Main 2021 (17 Mar Shift 2) · Chemistry

KBr is doped with 10-5 mole percent of SrBr2 The number of cationic vacancies in 1 g of KBr crystal is 1014. (Round off to the Nearest Integer). [Atomic Mass :  K=39.1u, Br=79.9u,NA=6.023×1023

Correct answer: 5

Solution

1 mole KBr (=119gm) have 10-5100 moles SrBr2 and hence, 10-7 moles cation vacancy (as 1Sr2+ will result 1 cation vacancy)

∴ Required number of cation vacancies

=10-7×6.023×1023119=5.06×1014≃5×1014

Hence, the correct answer is 5.

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