Final answer:
Calcium (Ca) and Potassium (K) are likely to form ionic bonds, while Oxygen (O) and Sulfur (S) are likely to form covalent bonds. Neon (Ne) does not normally form bonds.
Step-by-step explanation:
The two elements from O, Ne, S, Ca, and K that will most likely form an ionic bond are Ca and K, as they are metals with lower electronegativity and have a tendency to lose electrons to form cations. In contrast, the two non-metals O and S are likely to share electrons, thus forming a covalent bond. Ne, being a noble gas, typically does not form bonds because it already has a complete valence shell.