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

• A

  $1 a: \sqrt{3} a: \sqrt{2} a$
• Correct answer
  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

  $\frac{1}{2} \mathrm{a}: \frac{\sqrt{3}}{2} \mathrm{a}: \frac{\sqrt{2}}{2} \mathrm{a}$

Hence, the correct answer is option: 'B'.