Which substance is used in automobile air conditioning systems to create cold air?

The correct choice identifies that refrigerant is the substance used in automobile air conditioning systems to create cold air. Refrigerants are specifically designed for this purpose, functioning in a cycle of compression and expansion that absorbs and releases heat. This thermodynamic process allows the vehicle's air conditioning system to lower the temperature of the air circulating within the cabin.

When the refrigerant is compressed, it turns into a high-pressure gas that is then cooled down in the condenser. Once cooled, the refrigerant expands and evaporates, effectively absorbing heat from inside the vehicle and producing cold air that is blown into the cabin. The efficiency of this process, along with the specific properties of the refrigerant, makes it an essential component for effective cooling in automotive air conditioning systems.

Other substances listed have different primary functions. Coolant refers generally to liquids used to manage engine temperature rather than for thermoregulation within the air conditioning system. Propellant is typically associated with the propulsion of aerosols or gas-powered devices, while antifreeze is a fluid used to lower the freezing point of water in vehicle engines and is not involved in the air conditioning cooling cycle.