What do Dewar containers hold?

Dewar containers are specially designed vacuum flasks that are used to hold cryogenic liquids, which are substances that exist at extremely low temperatures. These containers consist of a double-walled structure with a vacuum between the walls, minimizing heat transfer and helping maintain the extremely low temperatures needed for cryogenic materials such as liquid nitrogen, helium, or oxygen. The design enables them to store these liquids safely and effectively, preventing them from vaporizing too quickly.

The other options do not align with the purpose and design of Dewar containers. Highly flammable gases, explosive materials, and corrosive chemicals require different containment methods and materials that are tailored to their specific hazards, making them unsuitable for storage in a Dewar container. This is why the correct answer focuses on cryogenic liquids, emphasizing the specialized function of Dewar containers in safely containing substances at very low temperatures.