Correct Answer is: (b) he will have to expend some energy to decrease I
Let L = angular momentum ω = angular velocity
I = moment of inertia.
Here, L is conserved. ∴ L = Iω = constant.
Kinetic energy =E = 1/2 Iω2 = 1/2 .I (L/I)2 = L2/2I
If I decreases, E increases. Hence, energy must be expended.