Explain why carbon dioxide is a gas at room temperature.?

Answer 1

Look at the VSEPR/Lewis structure:

O = C = O

The molecule is linear with no net dipole moment, because the polar bonds cancel each other out. It also has no hydrogen bond donor or acceptor sites.

It's also relatively light, with a molar mass of 44 g/mol.

Because of these molecular factors, it ends up being a gas at room temperature.

Answer 2

It has a boiling point below that of room temperature, meaning that it will evaporate at a lower temperature then say... water. And since room temperature is above it's boiling point, all the CO2 will be a gas at room temperature.