Why can air become liquid

The air we usually see is generally gas, and the water we see is generally in the form of liquid. This is because the temperature and pressure under natural conditions make air in the gas phase and water in the liquid phase. In fact, any substance can be in gaseous, liquid or solid state, as long as the pressure and temperature meet the requirements of the substance in this state. For example, when water is heated to 100 ℃ under standard atmospheric pressure, it can be turned into steam, and at 0 ℃, it can be turned into ice. In the same way, air can also be changed into liquid when it is cooled to minus 194 ℃ under standard atmospheric pressure. In fact, the state of matter is determined by pressure and temperature.