You're asking about the physical state of a substance at 20 degrees Celsius, but you haven't specified which substance!

To determine the physical state (solid, liquid, or gas) of a substance at 20 degrees Celsius, you need to know the melting point and boiling point of that substance.

Here's how to figure it out:

* If the melting point of the substance is below 20 degrees Celsius and the boiling point is above 20 degrees Celsius, it will be a liquid at 20 degrees Celsius.

* If the melting point of the substance is above 20 degrees Celsius, it will be a solid at 20 degrees Celsius.

* If the boiling point of the substance is below 20 degrees Celsius, it will be a gas at 20 degrees Celsius.

Example:

* Water: Melting point: 0 degrees Celsius, Boiling point: 100 degrees Celsius. Therefore, water is a liquid at 20 degrees Celsius.

Please tell me what substance you're interested in, and I can tell you its physical state at 20 degrees Celsius!