Which gas is evolved when metals react with acids to produce salts? 

Hydrogen gas 

The correct answer is option 1. Hydrogen gas.

Hydrogen gas is evolved when metals react with acids to produce salts. The general chemical equation for this reaction is:

\[ \text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen gas} \]

For example, when zinc reacts with hydrochloric acid:

\[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \]

In this reaction, zinc chloride (ZnCl₂) is formed, and hydrogen gas (H₂) is evolved.