Let I1 and I2 be the moments of inertia of two bodies of identical geometrical shape, the first made of aluminium and the second of iron.

Moment of inertia depends upon mass of object, geometry of the object, position of axis and distribution of mass around the axis. In the given question, the objects are identical in all respects, but their masses are different since and aluminium is lighter than iron, we can conclude that I1 < I2