To cause some gas to condense to a liquid, what must be done?

To cause gas to condense into a liquid, it is essential to remove heat from the gas. This process reduces the energy of the gas molecules, allowing them to come closer together and transition into a liquid state. When heat is removed, the thermal motion of the molecules decreases, promoting intermolecular forces that stabilize the liquid form.

In many cases, this removal of heat can be achieved by cooling the gas, which effectively lowers its temperature. Decreasing temperature directly contributes to the condensation process, as the gas molecules lose energy and the likelihood of them transitioning into a liquid increases.

The other methods, such as increasing pressure, may also facilitate condensation depending on the situation, but they are not the primary requirement for condensation itself. The core aspect lies in the removal of heat, which is the driving force for gas molecules to lose kinetic energy and successfully condense.