The region on the periodic table that contains mostly elements that are gases at room temperature is the rightmost column, also known as Group 18 or the noble gases.

Here's why:

* Noble gases are extremely unreactive due to their full outer electron shells.

* This lack of reactivity makes them exist as single atoms, which have weak interatomic forces.

* These weak forces allow them to easily overcome the attractive forces that would hold them together in a liquid or solid state at room temperature.

Let me know if you'd like more information about the periodic table or the properties of elements!