What makes up most of a calcium atom

Explanation:

The standard calcium isotope is ⁴⁰Ca. Because it is a calcium nucleus, WE KNOW that the nucleus contains 20 protons, 20 massive, positively-charged nuclear particles. The calcium nucleus also contains approx. 20 neutrons, 20 massive, neutrally-charged nuclear particles.

Because the calcium atom is neutral, also associated with the atom are 20 electrons, 20 negatively charged particles, of negligible mass, that are conceived to whizz about the massive nuclear core.

Hope this helps

3 hours because it is a decent distance.