Which of the following contribute(s) to most of the mass of an atom? O A) Protons and electrons
B) Protons only
C) Protons and neutrons
OD) Neutrons only

The nucleus inside an atom consists of positively-charged  protons  and neutrally-charged  neutrons. a  proton  is a subatomic particle with a positive electric charge. allprotons  are identical.

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom