What must happen to a gas before it can be condensed in a condenser?

For a gas to be effectively condensed in a condenser, it must first go through a process known as de-superheating. This occurs when the gas is cooled down from its superheated state, which is above its saturation temperature at a given pressure. When a gas is superheated, it exists at a temperature higher than the temperature at which it can transition to a liquid phase under the corresponding pressure.

De-superheating reduces the temperature of the gas to its saturation point, allowing it to begin the condensation process as it is brought in contact with a cooling medium in the condenser. Once the gas reaches this saturation point, it can release latent heat and change into a liquid phase effectively.

The other options may be involved in various stages of a gas's journey but are not prerequisites for condensation. Heating a gas would increase its temperature and inhibit condensation, expansion might lower its pressure and temperature but not directly facilitate condensation, and pressurizing the gas can lead to high thermal states that might also conflict with condensation unless de-superheating has already occurred.