Why is antifreeze added to water in car radiator to protect it What fact about the use of antifreeze illustrates a rule that governs the physical world?

This has got two properties in general.

For cooling only, then you need only water.

The problem with only water is when the car stand still with engine off in a cold environment. Water will eventually freeze, thus expand. This expansion will rupture the radiator and engine will quickly overheat because water runs out.

Only water might also corrode the inside surface of the radiator.

Most antifreeze liquids today offer frost-protection and corrosion-protection.

The antifreeze liquid just lowers the waters temperature-point of freezing.

Even when freezing (to a slurry) it does not form solid ice that can rupture the radiator.