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