Electron - In an atom, the central part which is composed of neutrons and protons including quarks is called the nucleus. Whereas the electron is the particle with negative elementary electric charge can be found inside the atom surrounding the nucleus.
The answer to your proposed question is Neutron. This is because the atomic mass unit of a neutron is 1 and so it would contribute to the overall mass of the atom.
I hope this answer helped you!
Answer:
I guess you mean by non element example. Non element examples have more than one elements. Carbon dioxide is a non element example since caebon dioxide has 2 oxygen atoms + 1 carbon atom = carbon dioxide.
I think catalyst is also a non element example because catalyst is inorganic which means that it is not a living thing. Since catalyst is in brass and brass is a non element example, I think catalyst is also a non element example.
Hope that helps, thank you !!