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  4. How many units of NaCl is present per unit cell of NaCl?

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Q. How many units of NaCl is present per unit cell of NaCl?

NTA AbhyasNTA Abhyas 2020The Solid State

Solution:

$Cl ^{-}$ions form $ccp$ lattice i.e 8 at corners +6 at face centres.
$\Rightarrow 8 \times \frac{8}{18}+6 \times \frac{1}{2}=4 Cl ^{-}$ions
$Na ^{+}$at octahedral voids 12 at centre edges plus one at body centre.
$\Rightarrow 12 \times \frac{1}{4}+1=4 Na ^{+} \text {ions }$
i.e $4 NaCl$ molecules per unit cell.
Solution