Question

How many unit cells are present in a cubic shaped ideal crystal of $NaCl$ of mass $1.0\, g$ ?

• A. $1.28 \times 10^{21}$ unit cells
• B. $1.71 \times 10^{21}$ unit cells
• C. $2.57 \times 10^{21}$ unit cells
• D. $5.14 \times 10^{21}$ unit cells

Answer 1

Answer: (C)

$n=4$ for $fcc$
Also no. of atoms in $1 \,g \,NaCl =\frac{6.023 \times 10^{23}}{58.5}$
No. of unit cells present in $1 \,g\, NaCl =\frac{6.023 \times 10^{23}}{58.5 \times 4}$
$=2.57 \times 10^{21}$ unit cells