Solid State - Result Question 35
35. A crystalline solid of a pure substance has a face-centred cubic structure with a cell edge of $400 $ $pm$. If the density of the substance in the crystal is $8 g $ $cm^{-3}$, then the number of atoms present in $256$ $ g$ of the crystal is $N \times 10^{24}$. The value of $N$ is
(2017 Adv.)
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Answer:
Correct Answer: 35. $(2)$
Solution:
- Density $(\rho)=8=\dfrac{4 \times M}{N _A\left(4 \times 10^{-8} cm\right)^{3}}$
$\Rightarrow M=128 \times 10^{-24} N _A \Rightarrow \text { No of atoms }=\dfrac{256}{M} \times N _A $
$=\dfrac{256}{128 \times 10^{-24} N _A} \times N _A=2 \times 10^{24}$
BETA
