The two are potassium and rubidium. Why? Na is an alkali metal. As you go down the metals become more reactive. Calcium has 20 protons. Why? The atomic # is 20 (the one at the top). It has 20 neutrons. Why? The atomic mass (the number on the bottom) is ~40, ignoring electron mass. 40- 20 protons = 20 neutrons. It has 20 electrons. Why? The # of protons and electrons is the same. Ions aren't on the periodic table.Please mark brainliest if I helped you!
