Statement 1: Sun is the heaviest object in Solar system.
Statement 2: Size of Sun is much bigger than Earth.
Both the statements are true. Statement 2 is not correct explanation of statement 1.
Sun is the heaviest object in the Solar system. But mass depends on density and volume of the object. A neutron star whose size is much lesser than Sun can be heavier than Sun beacuse the density of neutron star is much higher than Sun.