Answer:
Acid
Step-by-step explanation:
Metal oxides are basic in nature. So if an acid reacts with a metal oxide neutralization reaction takes place. In these types of reactions respective salt and water are formed.
Acid + Metal Oxide ⇨ Salt + Water
Example:
Calcium is a metal, thus calcium oxide is a metallic oxide which is basic in nature. When an acid; such as hydrochloric acid; reacts with calcium oxide, neutralization reaction takes place and calcium chloride; along with water; is formed.