Q22 / 160 · TS EAMCET 2020 (09 Sep Shift 2) · Chemistry
If the distance between $\mathrm{Na}^{+}$and $\mathrm{Cl}^{-}$ions in sodium chloride crystal is ' $Y$ ' $\mathrm{pm}$. The length of the edge of the unit cell will be
- A$4 Y \mathrm{pm}$
- Correct answerB$2 \mathrm{Y} \mathrm{pm}$
- C$\frac{Y}{4} \mathrm{pm}$
- D$\frac{\mathrm{Y}}{2} \mathrm{pm}$
Solution
$\because$ In sodium chloride crystal, the distance
$\because \mathrm{NaCl}$ has fec structure in which $\mathrm{Na}^{+}$occupies all octahedral voids, while $\mathrm{Cl}^{-}$ions are present at all corners and edge centers.
If, edge length $=a$
The distance between $\mathrm{Na}^{+}$and $\mathrm{Cl}^{-}=Y$ pm (Given)
$a=2\left(r_{\mathrm{C}^{-}}+r_{\mathrm{Na}^{+}}\right)=2 Y \mathrm{pm}$
Hence, edge length is $2 Y$ pm and option (b) is the correct answer.
Hence, the correct answer is option: 'B'.