An ionic compound crystallises in FCC type structure with ‘A’ ions at the centre of each face and ‘B’ ions occupying corners of the cube. The formula of compound is _______.

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KollegeApply · Accepted Answer

'A' ions are at the centre of each face. There are six face centres and each contributes one half to the unit cell. Total number of A ions present per unit cell =6 xx $\frac{1}{2}$ = 3. 'B' ions occupy corners of the cube. There are 8 corners and each contributes one eight to the unit cell. Total number of B ions present per unit cell =8xx1/8=1. The formula of a compound is A3B Hence, the correct answer is A3B.

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