In which state does one pound of refrigerant occupy the most space?

One pound of refrigerant occupies the most space in the vapor gas state due to the molecular arrangement and the distance between molecules. In this state, the refrigerant exists as a gas, where the molecules are in a high-energy state and are far apart compared to liquids.

In contrast, when refrigerants are in a liquid state, the molecules are closely packed together, resulting in a much smaller volume occupancy. Even in a saturated liquid state, where the refrigerant is at its boiling point and is transitioning between liquid and gas, the volume will still be smaller compared to vapor gas since the molecules are still relatively compact.

In the saturated vapor state, the refrigerant is close to becoming liquid again and has more space between molecules compared to a liquid state but still not as much as in the vapor gas state. Therefore, as the refrigerant transitions into vapor gas, the volume occupied by one pound significantly increases due to the increased distance between the molecules, leading to maximum expansion and the least density.