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Q.
How many units of $NaCl$ is present per unit cell of $NaCl$?
NTA AbhyasNTA Abhyas 2022
Solution:
$Cl^{-}$ ions form ccp lattice i.e 8 at corners + 6 at face centres.
$\Rightarrow 8\times \frac{1}{8}+6\times \frac{1}{2}=4 \, Cl^{-} \, ions$
$Na^{+}$ at octahedral voids 12 at centre edges plus one at body centre.
$\Rightarrow 12\times \frac{1}{4}+1=4Na^{+} \, ions$
i.e $\text{4NaCl}$ molecules per unit cell.
