Juan argues that electron account for the most mass in an atom because they take up the most space. julie disagrees. who do you agree with

It is true that the electrons in an atom accounts for the most of volume of the atom. However, most of the mass of atoms is due to protons and neutrons that are localized at the center in atom, i.e nucleus. Hence, electrons account for atomic volume; while the nucleus of atoms dictates it's mass.