Question

How many unit cells are present in a cube-shaped ideal crystal of $\text{NaCl}$ of mass $1.00$ g?

• A. $1.03\times {10}^{22}$ unit cells
• B. $2.57\times {10}^{21}$ unit cells
• C. $1.28\times {10}^{21}$ unit cells
• D. $1.71\times {10}^{21}$ unit cells

Answer 1

The correct option is B $2.57\times {10}^{21}$ unit cells

One unit of $\text{NaCl}$ contains $4$ $\text{NaCl}$ molecules $=\frac{4\times 58.5}{6.023\times {10}^{23}}$ g

Number of unit cells in $1$ g $=\frac{6.023\times {10}^{23}}{4\times 58.5}⟹2.57\times {10}^{21}$