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JEE Advanced levelSingle correct optionDifficulty 3 of 3ss177

In a compound the anions $X$ form a ccp lattice and the cations $Y$ occupy three-fourths of the tetrahedral voids. The formula of the compound and the number of cations per unit cell are

A $YX$ , 8
B $Y X_{3} X X_{2}$ , 6
C $Y X_{3} X X_{2}$ , 8
D $Y X_{2} X X_{3}$ , 6

Answer: B

ccp gives 4

X

per cell and 8 tetrahedral voids. Three-fourths of 8 is 6 cations

Y

, so the ratio

Y : X = 6 : 4 = 3 : 2

and the formula is

Y X_{3} X X_{2}

with 6 cations per cell.

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