Question

long type of question, how can we liquefy a gas? Give example

Answer 1

by applying pressure reducing temperature

Answer 2

we can liquefy a gas by increasing pressure
Here's a activity to show that how gas liquefied.

In a gas cylinder the air is stored.The air is given a pressure by a piston.As the particles of gas are highly compressible when the piston pressurises it the particles of gas come closer to each other.This changes the state of the gas and liquefies it.

Applying pressure and reducing temperature can liquefy gases

If we reduce temperature condensation will take place and the gas or vapour changes into liquids.

hope it helps you