Which of the following best describes a steam boiler?

A steam boiler is defined as a vessel that utilizes water and fuel to generate steam. This process involves heating the water to its boiling point, allowing it to convert into steam, which can then be used for various applications such as heating, power generation, or industrial processes. The essential function of a steam boiler is its ability to efficiently produce steam through the combination of water and a fuel source, often employing mechanisms like burners or heating elements to facilitate this conversion.

In contrast, the other options do not accurately capture the primary characteristics of a steam boiler. For instance, specifying a device that transfers heat by circulating air pertains more to air heating systems rather than steam generation. Similarly, a system that heats water without producing steam describes water heaters rather than steam boilers, which inherently involve steam production. Lastly, while a container that stores steam for industrial use hints at a steam-related function, it does not encompass the fundamental operation of creating steam from water and a fuel source, which is critical to a steam boiler's definition.