What happens to the liquid in the delivery line upon completing the delivery of metered cryogenic liquid?

When the delivery of metered cryogenic liquid is completed, the process results in a drop in pressure within the delivery line. This reduction in pressure allows the cryogenic liquid to vaporize, leading to the formation of gas. In this scenario, the vaporization generates pressure that can force the liquid from the line into the receiving container.

This phenomenon occurs because cryogenic liquids, when subjected to pressure changes, can quickly transition from a liquid state to a gaseous state. As the liquid vaporizes, if the pressure in the line is sufficiently low compared to the vapor pressure of the cryogenic liquid, the vaporization not only happens at the end of the delivery, but it can also facilitate the movement of remaining liquid in the line into the receiving container.

Given this understanding, the correct answer reflects the behavior of cryogenic liquids at the conclusion of a delivery where the drop in pressure and subsequent vaporization cause movement of the liquid into the receiving vessel. The other options do not accurately represent the typical behavior seen in cryogenic delivery processes, such as immediate vaporization without any flow, backflow to the pump, or the liquid remaining stationary due to temperature equalization, which would not occur under these delivery conditions.