Cryogenic liquids are defined as those existing at temperatures below which threshold?

Answer: C — -238°F

Cryogenic liquids are defined by their extremely low boiling points at standard pressure. The commonly used cutoff is below -150°C, which is -238°F. That boundary is the line used to categorize a liquid as cryogenic for safety and handling purposes. So the threshold value is -238°F. Liquids with boiling points colder than this (below the line) are considered cryogenic. For example, liquid nitrogen boils at -196°C (-321°F), which sits well into the cryogenic range. Values warmer than the boundary, like -196°F (-122°C) or -130°F (-90°C), do not meet the cryogenic cutoff.