Which of the following statements is not true about NaCl structure?

Options

A. `Cl^(-)` ions are in fccarrangement
B. `Na^(+)` ions has coordination number 4
C. `Cl^(-)` ions has coordination number 6
D. Each unit cell contains 4NaCl molecules

Answer

B

Explanation

Position of `Cl^(-)` ions :At the corners (8 nos.) and at the face centres (6 nos.).
Position of `Na^(+)` ions : At the edge centres (12 nos.) and at the body centre (1 no.)
(a) `Cl^(-)` ions are in fcc arrangement.
(b) The `Na^(+)` ion at body centre ) (X is surrounded by `6Cl^(-)` atoms, so the C.N. is 6.
(c) Any `Cl^(-)` ion (say at Y) is surrounded by `5Na^(+)` atoms in this cell and one more from the adjacent cell.
So C.N of `Cl^(-)` is 6 .
(d) Effective no. of `Cl^(-)` ions = `8 xx 1//8 + 6 xx 1//2 = 4`
Effective no. of `Na^(+)` ion = `12 xx 1//4 + 1 xx 1 = 4`
So each unit cell contains 4NaCl molecules.