Answer:
Magnesium
Step-by-step explanation:
The element that could provide one atom to make an ionic bond with oxygen is magnesium.
Generally, most group II elements will form an ionic bond with oxygen with just one atom.
An ionic bond forms by the transfer of electrons from one specie to another.
Oxygen has a charge of 2-, to use one atom to form ionic bond with this specie, a magnesium atom with 2+ charge will bond with the specie.
This will form:
MgO
This is notable for other group II elements.