A cylinder is inscribed in a sphere of radius $r$. What is the radius of the cylinder of maximum volume?

• A

  $\frac{2 r}{\sqrt{3}}$
• Correct answer
  B

  $\frac{\sqrt{2} r}{\sqrt{3}}$
• C

  $r$
• D

  $\sqrt{3} r$

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