A spherical ball of radius 3 cm is melted and recast into three spherical balls.

(c) 2.5 cm

Let r cm be the radius of the third ball.
Volume of the original ball = volume of the three balls

$\frac{4}{3} \pi \times 3^{3}=\frac{4}{3} \pi \times 1.5^{3}+\frac{4}{3} \pi \times 2^{3}+\frac{4}{3} \pi r^{3}$

$\Rightarrow 27=3.375+8+\mathrm{r}^{3}$

$\Rightarrow r^{3}=27-11.375=15.625$

$\Rightarrow r=2.5 \mathrm{~cm}$