Answer:
C. Bromine
Explanation:In ionic bond , the metals looses electron and the non metal gains electron.
In the given options ;
Aluminum (Al)= METAL
Copper (Cu) = METAL
Bromine (Br) = NON METAL
Oxygen (O) = NON METAL
That leaves us with bromine and oxygen.
Oxygen has an electronic configuration of 2,6.(see image).
So oxygen needs to gain two electrons.
Bromine has one valence electron ( see image).
So therefore , Bromine needs to gain one electron as It is in Group VII
