Answer: a. BaO
Explanation:
For formation of a neutral ionic compound, the charges on cation and anion must be balanced. The cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals.
Here element barium is having an oxidation state of +2 called as [tex]Ba^{2+}[/tex] cation and [tex]O^{2-}[/tex] is an anion with oxidation state of -2. Thus they combine and their oxidation states are exchanged and written in simplest whole number ratios to give neutral [tex]BaO[/tex]
