Explanation:
Atoms that share electrons with each other tend to form a covalent bond. Whereas atoms that show transfer of electrons from one atom to another tend to form an ionic bond.
Sodium has atomic number 11 and oxygen has atomic number 8. In order to become stabilized, sodium needs to lose one electron whereas oxygen needs to gain two electrons. So, two sodium atoms will combine with one atom of oxygen. This will form an ionic bond between sodium and oxygen atom.
Carbon has atomic number 4 and fluorine has atomic number 9. Therefore, both of them will share electrons in order to become stabilized. Thus, they will form a covalent bond.
Oxygen atom has atomic number 8 and hydrogen has atomic number 1. Therefore, both of them will share electrons but due to difference in electronegativity of both hydrogen and oxygen they will result in the formation of a polar covalent bond.
Aluminium has atomic number 13 and chlorine has atomic number 17. So, aluminium will donate or transfer its valence electron to chlorine atom. Therefore, it will also form an ionic bond.
Thus, we can conclude that carbon (C) and fluorine (F) and oxygen (O) and hydrogen (H) are the combination(s) that would result in sharing of electrons.