What is produced when a metal oxide reacts with an acid?

When a metal oxide reacts with an acid, the products of the reaction are a salt and water. This is based on the neutralization reaction that generally occurs between an acid and a base. In this case, the metal oxide acts as a base.

The generic reaction can be written as:

[ \text{Metal Oxide} + \text{Acid} \rightarrow \text{Salt} + \text{Water} ]

For example, if you take copper(II) oxide and react it with hydrochloric acid, the reaction yields copper(II) chloride (the salt) and water. This showcases how metal oxides, which are basic in nature, react with acidic substances to form neutral products (salt and water).

The other options suggest that only a salt or water is produced, or that hydrogen gas is evolved, which does not happen in this specific type of reaction. The formation of hydrogen gas typically occurs when certain metals react with acids, but metal oxides do not release hydrogen gas; rather, they undergo a neutralization process with acids, leading to the formation of salt and water.