The volume of a right circular cone which is obtained from a wooden cube of edge 4.2 dm wasting minimum amount of wood is :

Answer: Option C

The volume of cone should be maximum
∴ Radius of the base of cone :
$$\begin{array}{rl}& =\frac{\text{Edge of cube}}{2}\\ & =\frac{4.2}{2}\\ & =2.1\text{dm.}\end{array}$$
Height of cone = Edge of cube = 4.2 dm.
∴ Volume of cone :
$$\begin{array}{rl}& =\frac{1}{3}\pi r^{2}h\\ & =\left(\frac{1}{3}\times \frac{22}{7}\times 2.1\times 2.1\times 4.2\right)\text{cu}\text{.dm}\text{.}\\ & =19.404\text{cu}\text{.dm}\text{.}\end{array}$$