Question

The number of unit cells in $58.5g$ of $NaCl$ is approximately

• A. $6\times {10}^{20}$
• B. $1.5\times {10}^{23}$
• C. $6\times {10}^{23}$
• D. $0.24\times {10}^{24}$

Answer 1

The correct option is B $1.5\times {10}^{23}$

Atomic mass of $\text{NaCl}=58.5\text{g/mol}$

Weight of $\text{NaCl}$ given $=58.5\text{g}$

Mole of $\text{NaCl}=\frac{58.5}{58.5}=1\text{mole};$

No. of atoms $=1\times 6.022\times {10}^{23}$

$\text{NaCl}$ has $\text{fcc}$ unit cell which has $4$ atoms per unit cell.

Therefore, Number of unit cells

$\Rightarrow \frac{6.022\times {10}^{23}}{4}$

$\Rightarrow 1.5\times {10}^{23}$

Hence, the correct option is $\text{B}$