If a gas with an odor is released in a room, it can quickly be detected across the room because it

Diffuses

Explanation:

Diffusion is the movement in which anything (atoms, molecules, ions) will travel from higher concentration to lower concentration. Gradient concentration is necessary to make diffusion. If we released a gas with an odour in a room, the highest concentrated area where the gas was released. So the gas particles will move and spread all over the room because of the lower concentration of this gas in those places. As a result, we smell the gas.