A cone and a hemisphere have equal bases and equal volumes.

(b) 2 : 1

Let the radii of the cone and the hemisphere be r and their respective heights be h and H.

Then $\frac{1}{3} \pi \times r^{2} \times h=\frac{2}{3} \pi \times r^{2} \times H$

$\Rightarrow \frac{h}{H}=\frac{2}{1}$