The correct answer is C because [tex]BaO[/tex] has the chemical name barium oxide, the hydroxide part is only when we have an [tex]OH^-[/tex] ion attached to the metal. HF is called hydrogen fluoride as opposed to the mono hydrogen mono fluoride. The exceptions in nomenclature for covalent compounds is to never use mono for the first element of a covalent compound and never to use a prefix for a hydrogen containing compound.
