What type of materials are typically stored in cylinders?

Cylinders are specifically designed to safely contain gases and liquids under pressure. This includes a wide range of substances, such as industrial gases (like oxygen, nitrogen, and propane) and liquids that may be gasified (such as liquefied petroleum gas). The pressure inside these cylinders can vary, but these materials are stored in a way that prevents leaks and ensures safety during handling and transport.

In contrast, liquids under atmospheric pressure typically do not require high-pressure containers like cylinders, as they can be stored in tanks or other vessels that don't need to withstand the same pressures. Solid chemicals are usually stored in bags, drums, or bins rather than cylinders, as they do not require the pressure containment that gases do. Biological materials may have specific containment requirements that do not involve the use of cylinders unless they are under pressure or in a research context, but they are generally housed in secure biological containers designed for that purpose.

Thus, the correct answer highlights that cylinders are primarily utilized for gases and liquids that are stored under pressure, ensuring their safe storage and transport.