Question

If all the face centred atom occupied by $C{l}^{-}$ are replaced by $N{a}^{+}$ atom. Then the chemical formula of the unit cell is:

• A. $NaCl$
• B. $N{a}_{7}Cl$
• C. $N{a}_{4}Cl$
• D. none of these

Answer 1

The correct option is B $N{a}_{7}Cl$

If all the face centered atoms are replaced by Na+, then number of ${Cl}^{-}$ atoms =

$8\times \frac{1}{8}=1\downarrow corners$

and no. of $N{a}^{+}$ atoms =

$12\times \frac{1}{4}+1\times 1+6\times \frac{1}{2}=7\downarrow \downarrow \downarrow edgesbodyreplacedcenter$

so the cemical formula will become ${Na}_{7}Cl$

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