Answer:
Ar
Step-by-step explanation:
A neutral calcium atom would have the same number o electrons as protons. Ca has an atomic number of 20, which means it has 20 protons. A neutral Ca atom would also have 20 electrons. This one, Ca²⁺, is missing 2 electrons, which is why is has a +2 charge. That means it only has 18 electrons. A neutral element having 18 electrons also has 18 protons. Element 18 is Argon (Ar).