Here's why:

* Oxygen molecules (O2) are small and nonpolar. They have a symmetrical structure, meaning the electrons are distributed evenly. This results in weak London Dispersion Forces (LDFs) as the only intermolecular force between them. LDFs are temporary attractions that arise from fluctuating electron clouds.

* The LDFs between oxygen molecules are very weak. This is because the molecules are small and the electrons are tightly held.

* Weak intermolecular forces mean that the oxygen molecules can easily overcome the attraction to each other and move freely. This is why oxygen exists as a gas at room temperature.

Let's contrast this with other substances:

* Water (H2O) is a liquid at room temperature. It has stronger hydrogen bonds between molecules, which are more significant than the LDFs in oxygen.

* Sodium chloride (NaCl) is a solid at room temperature. It forms a crystal lattice with strong ionic bonds, holding the molecules together tightly.

In summary, oxygen's gaseous state at room temperature is a result of its small size, nonpolar nature, and the weak London Dispersion Forces between its molecules.