Answer: By applying pressure and decreasing temperature.
Step-by-step explanation:
To liquefy atmospheric gases means to convert the state of gases into liquids.
In gases, particles are very far away and to make the particles come closer to each other, we need to apply pressure to the gas particles.
The particles can be brought closer by decreasing the pressure of the system.
Hence, by applying pressure and decreasing temperature, atmospheric gases can be liquefied.