Chlorine is a gas at 21 degrees Celsius (70 degrees Fahrenheit).

Here's why:

* Chlorine's boiling point is -34.04 °C (-29.27 °F). This means that chlorine will be a gas at temperatures above its boiling point.

* 21 °C is significantly higher than chlorine's boiling point. Therefore, chlorine will be in its gaseous state at this temperature.