The correct answer is B) holds the entire refrigerant charge after system pump down. The receiver in a refrigeration system acts as a storage tank to hold the entire refrigerant charge after the system has been pumped down. This allows the compressor and other components to be serviced or repaired without losing the refrigerant. The receiver ensures that the refrigerant charge is contained and available to be returned to the system when needed. The other answer choices are incorrect because: A) the superheating function is performed by the expansion valve, not the receiver; C) the receiver does not directly prevent liquid refrigerant from flooding the compressor, that is the role of the expansion valve; and D) the receiver does not collect air and non-condensable gases, those are typically removed by the system's purge or drier components.