If the rate of change of volume of a sphere is the same as rate of change of its radius, then radius is equal to:

1 $\frac{1}{2\sqrt{π}}$ $\sqrt{2π}$ Arbitray

$\frac{1}{2\sqrt{π}}$

$V=\frac{4}{3}πr^3;\frac{dV}{dt}=\frac{4}{3}π×3r^2\frac{dr}{dt}=\frac{dr}{dt}⇒r=\frac{1}{2\sqrt{π}}$