Question

what is the size of nucleus of an atom

Answer 1

10^-15 m or 1 fermi is the size of nucleus

Answer 2

The size (diameter) of the nucleus is between 1.6 fm (10−15 m) (for a proton in light hydrogen) to about 15 fm (for the heaviest atoms, such as uranium). These sizes are much smaller than the size of the atom itself by a factor of about 23,000 (uranium) to about 145,000 (hydrogen). Although it is only a very small part of the atom, the nucleus has most of the mass.