Answer the following question given this paragraph: 

You already know that a sour taste is one property of acids. ( Warning : Never taste an unknown substance to see whether it is an acid!) Acids have certain other properties as well. For example, acids can conduct electricity when dissolved in water because they consist of charged particles in solution. (Electric current is a flow of charged particles. ) Acids can also react with metals, and when they do they produce hydrogen gas. An example of this type of reaction is hydrochloric acid reacting with the metal zinc (Zn). The reaction is pictured in the Figure below . It can be represented by the chemical equation:.


Q: Acids can also react with metals, and when they do they produce what?

 Choices:

- alloys

- potassium gas

- rust

- hydrogen gas

A:
hydrogen gas
