True.
Let the radius of the sphere and cylinder be r.
Given, height of the cylinder = diameter of the base
⇒h=2r
Radius of sphere = Radius of cyllinder = r
According to the given condition,
Volume of sphere
=23×Volume of cylinder
⇒43πr3=23×πr2×2r
⇒43πr3=43πr3
Hence, volume of the sphere is equal to two-third of the volume of a cylinder