Final answer:
Calcium most likely forms the calcium cation, Ca²+, by losing two electrons to achieve the stable electron configuration of the noble gas argon.
Step-by-step explanation:
The ion that Calcium is most likely to form is the calcium cation, denoted as Ca²+. Calcium is a group 2 alkaline earth metal, which means it readily loses two electrons to form a cation with a 2+ charge. This occurs because atoms aim to achieve the electron configuration of the noble gas that precedes them in the periodic table. For calcium, that noble gas is argon, so when calcium loses two electrons, it has the same electron configuration as argon (1s² 2s² 2p⁶ 3s² 3p⁶), resulting in a stable Ca²+ ion.