Final answer:
The weight of liquid oxygen per gallon depends on temperature and pressure and cannot be accurately determined without specific conditions.
Step-by-step explanation:
Liquid oxygen weighs approximately 70.99 grams per mole. To convert this to weight per gallon, you would need to know the volume of a gallon of liquid oxygen. Unfortunately, the volume of liquid oxygen can vary depending on temperature and pressure. Therefore, it is not possible to provide an accurate answer to how much liquid oxygen weighs per gallon without specific temperature and pressure conditions.