The four identical uniform solid spheres are shown below. The radius of each sphere is R. Lets take centre of the system at O.
Then, distance from the centre for rB=rC and rA=rD ∴ Moment of inertial, M0I=Mr2, for each spheres will be IA,IB,IC and ID. ∴‌‌IA=ID and IB=IC Since, ‌‌rB=rC<rA=rD Therefore, ‌‌IA=ID>IB=IC