What happens to air as it is compressed?

When air is compressed, the process causes the air molecules to be squeezed closer together, leading to an increase in kinetic energy among the molecules. This increase in kinetic energy raises the temperature of the air, which means that it becomes heated.

This is a fundamental principle of thermodynamics known as the ideal gas law, where pressure and temperature have a direct relationship: as the pressure on a gas increases, so does its temperature, provided the volume remains constant. This heating effect is often experienced in applications involving air compressors, where the air exiting the compressor is significantly warmer than the air entering it.

The other choices do not accurately describe the behavior of air during compression. For example, while air can condense under certain circumstances when cooled, the immediate effect of compression itself is heating, not cooling or condensing. Similarly, while air can expand when pressure is released, the action of compression specifically involves reducing volume and increasing temperature, rather than expansion.