Question

The number of unit cells present in $39 \,g$ of potassium if it crystallizes as body centred cube is
$(N=$ Avogadro number, At. wt. of potassium $=39$ )

• A. $\frac{N}{4}$
• B. $\frac{N}{2}$
• C. $\frac{N}{3}$
• D. $N$

Answer 1

Answer: (B)

Potassium has bcc system

Number of mole $=39 / 39=1$ mole

$1$ mole of atoms $=6.022 \times 10^{23}$ atoms $=N$

$\because$ In bcc system $2$ atoms are present in $1$ unit cell.

$\therefore N$ number of atoms are present in $\frac{N}{2}$ unit