Question

What is the number of atoms present per unit cell of aluminium having edge length 4 Å?

Options

• 4

• 1

• 8

• 2

Answer 1

4

Explanation:

a = 4 Å = 4 × 10^-8 cm, ρ = 2.7 g cm^-3,

M = 27, n = ?

n = `(rho xx "a"^3 xx "N"_"A")/"M"`

`= (2.7 xx (4 xx 10^-8)^3 xx 6.022 xx 10^23)/27`

= 3.85 i.e. 4