If the height and the radius of a cone are doubled, the volume of the cone becomes

(d) 8 times

Let the new height and radius be 2h and 2r, respectively.

New volume of the cone $=\frac{1}{3} \pi(2 r)^{2} \times 2 h$

$=\frac{8}{3} \pi r^{2} h=8 \times$ initial volume of the cone