Choose the most appropriate answer from the following list of oxides which fit the description. Each answer may be used only once :
[SO2, SiO2, Al2O3, MgO, CO, Na2O]
(i) A basic oxide.
(ii) An oxide which dissolves in water forming an acid.
(iii) An amphoteric oxide.
(iv) A covalent oxide of a metalloid.
