How many molecules are there in the unit cell of sodium chioride?

Options

A. `2`
B. `4`
C. `6`
D. `8`

Answer

b

Explanation

In `NaCI` (rock salty)
Number of `Na^(+)` ions `= 12` (at edge centers ) `xx (1)/(4) xx 1` (at body centers ) `xx 1 = 4 `
Number of `CI^(-)` ions `= 8` (at centers )`xx (1)/(8) xx 6` (at face centers ) `xx (1)/(4)`
Thus `4` formula units per unit cell