The aqueous solution of the oxide turns blue litmus paper red. This means the aqueous solution is acidic in nature. Metals react with oxygen to form metallic oxides. These metallic oxides are basic because they react with water to form bases. On the other hand, nonmetals react with oxygen to form nonmetallic oxides. These oxides are different from metallic oxides because they are acidic in nature. Nonmetallic oxides react with water to form acids. Since, the aqueous solution of this oxide is acidic in nature, the element is a nonmetal. For example, Sulphur is a nonmetal. It will form an oxide called sulphur dioxide which is acidic in nature.