The Dewar flask is best described as which of the following?

• A. A device for storing dry ice
• B. A vessel for insulating liquids
• C. A vessel for storing liquid oxygen
• D. A container for storing compressed air

Answer: (C)

A Dewar flask is designed to keep very cold liquids from warming up. It uses a double wall with a vacuum between them to minimize heat transfer, so cryogenic liquids can be stored for long periods without evaporating quickly. Because of this, its main use in practice is to hold extremely cold liquids such as liquid oxygen, which is a common cryogenic liquid in welding and related fields. That makes describing it as a vessel for storing liquid oxygen the best fit among the options. The other choices miss the key point that the Dewar’s purpose is cryogenic storage, not just general insulation, dry ice storage, or containing compressed air.