What does lowercase r mean

The transfer of heat through the movement of a gas or liquid a. convection b. conduction c. radiation

True or false when elements combine to form a mixture, the resulting chemical properties may be very different from those of the elements that make it.

Africtionless piston-cylinder contains 50 l of saturated liquid r-134a. the piston has a mass and an area resulting in an applied pressure of 500 kpa on the refrigerant. the refrigerant is now heated until its temperature rises to 70∘c. calculate the work (in kj) done during this process.