Where is the majority of the mas located in the atom?

The majority of an atom's mass is concentrated in its nucleus, which is composed of protons and neutrons. Protons have a positive charge and neutrons have no charge, together making up nearly all of the atom's mass. In contrast, the electrons, which orbit the nucleus, contribute very little to the overall mass of the atom. Thus, while the nucleus is small relative to the entire atom, it contains the vast majority of its mass.