3. Hydrochloric acid is used to clean metals.

The acid reacts with the oxide layer on the surface of the metal, forming a salt and water.

Which word describes the metal oxide?

A alloy

B base

C element

D indicator

Base

Explanation:

Acid + Base ⇒ Salt + Water (Neutralization Reaction)

So the substances forming salt and water must be acid and base.

Since HCl is acid so the Metal Oxide would be the base.

The answer to your question is option b, a base. This is because the question clearly tells you that one reactant is an acid. Then, it tells you that an acid plus something gives you a salt and water, as products

From background knowledge, we know that a base plus acid gives you a salt and water. The hydroxide ions from the base neutralise the hydrogen ions from the acid, which gives you water (as it has a pH of 7).

Therefore, your answer is b, a base