Question

The number of unit cells present in $39grams$ 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)

$\frac{N}{2}$

The number of moles of K $=\frac{39g}{39g/mol}=1mol$
1 mole of K will contain N atoms where N is Avogadro number. A bcc unit cell contains 2 K atoms. The number of unit cells present in 39 grams of Potassium if it crystallizes as body centred cube is $\frac{N}{2}$