Final answer:
The liquid helium is stored in a perfect blackbody radiator spherical container surrounded by a vacuum to minimize heat transfer by conduction and convection.
Step-by-step explanation:
The liquid helium is stored at its boiling point temperature of 4.2K in a spherical container that is a perfect blackbody radiator. The container is surrounded by a. Vacuum, which is the most suitable option as it minimizes heat transfer by conduction and convection. A vacuum reduces the temperature difference between the liquid helium and the surroundings, thus helping to maintain the low temperature efficiently.