What class of elements includes all of the elements that are gases at room temperature? nonmetals metals metalloids?

Metals have high density. They are always solids at room temperature.

Metalloids have intermediate density. They are generally solids at room temperature.

Non-metals have low density. They can be solids, liquids or gases at room temperature.

Based on this, the class of elements that includes all of the elements that are gases at room temperature is the non-metals