Answer:
Option B
Explanation:
Here, volume of cylindrical container,
V= πr2h .............(i)
and let volume of the material used be T.

∴T=π[(r+2)2−r2]h+π(r+2)2×2
T=π[(r+2)2−r2]Vπr2+2π(r+2)2
[∵V=πr2h⇒h=Vπr2]
⇒T=V(r+2r)2+2π(r+2)2−V
On differentiating w.r.t , we get
dTdr=2V.(r+2r).(−2r2)+4π(r+2)
At, r=10, dTdr=0
Now, 0=(r+2).4(π−Vr3)
⇒ Vr3=π, where r=10
⇒ V1000=π,orV250π=4