* Ionic bonds form between elements with a large difference in electronegativity. Electronegativity is the ability of an atom to attract electrons.

Let's analyze each option:

* a) Silicon and oxygen: Silicon and oxygen have a significant electronegativity difference, but they tend to form covalent bonds (sharing electrons) rather than ionic bonds. Silicon dioxide (SiO2), also known as silica, is a network covalent compound.

* b) Carbon and hydrogen: Carbon and hydrogen have a relatively small electronegativity difference, leading to the formation of covalent bonds in hydrocarbons.

* c) Magnesium and oxygen: Magnesium is a metal with a low electronegativity, while oxygen is a nonmetal with a high electronegativity. This large electronegativity difference makes them highly likely to form an ionic bond. Magnesium readily loses two electrons to become a +2 cation (Mg²⁺), while oxygen gains two electrons to become a -2 anion (O²⁻), forming the ionic compound magnesium oxide (MgO).

Therefore, magnesium and oxygen are the most likely to form an ionic bond.