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Question: Answered & Verified by Expert
If 'a' stands for the edge length of the cubic systems : simple cubic, body centred cubic and face centred cubic, then the ratio of radii of the spheres in these systems will be respectively
ChemistrySolid StateNEETNEET 2008 (Mains)
Options:
  • A $1 a: \sqrt{3} a: \sqrt{2} a$
  • B $\frac{1}{2} a: \frac{\sqrt{3}}{4} a: \frac{1}{2 \sqrt{2}}^a$
  • C $\frac{1}{2} a: \sqrt{3} a: \frac{1}{\sqrt{2}} \mathrm{a}$
  • D $\frac{1}{2} \mathrm{a}: \frac{\sqrt{3}}{2} \mathrm{a}: \frac{\sqrt{2}}{2} \mathrm{a}$
Solution:
2442 Upvotes Verified Answer
The correct answer is: $\frac{1}{2} a: \frac{\sqrt{3}}{4} a: \frac{1}{2 \sqrt{2}}^a$
For simple cube, $a=2 r$
or $r=\frac{a}{2}$
For BCC, $4 r=\sqrt{3} a$
or $r=\frac{\sqrt{3}}{4} a$
For FCC, $4 r=\sqrt{2} a$
or $r=\frac{a}{2 \sqrt{2}}$
Thus, the ratio is $\frac{1}{2} a: \frac{\sqrt{3}}{4} a: \frac{1}{2 \sqrt{2}} a$

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