Ncert Exercises & Solutions

The number of tetrahedral voids per unit cell in NaCl crystal is -

I. 4

II. 8

III. Twice the number of octahedral voids

IV. Four times the number of octahedral voids.

The correct choice among the given is-

1. (I, II)

2. (II, III)

3. (III, IV)

4. (I, IV)

Hint: Tetrahedral void is double the number of Cl atoms in a unit cell

NaCl has a rock salt type structure having fcc arrangement.

Total number of atoms per unit cell = 4

∴

Number of tetrahedral voids = 2 x 4= 8

Number of octahedral voids = 4

Tetrahedral void double of the octahedral void.

Hence, option second is correct answer.