What process occurs in a boiler to generate steam?

The correct choice is based on the fundamental operation of a boiler, which is designed to convert water into steam through heating. In this process, water is heated to its boiling point, where it undergoes a phase change from liquid to gas. When water reaches this temperature, the molecules gain enough energy to break free from their liquid state, allowing steam to be produced. This steam can then be utilized for various applications, including heating, powering turbines, and other industrial processes.

Heating water to its boiling point is essential because only at this temperature does water transition into steam effectively. The production of steam under controlled conditions also facilitates the generation of pressure within the boiler system, which is critical for efficient energy transfer and usage.

Other options suggest processes that do not accurately represent how steam generation occurs in a boiler. For instance, condensing water, mixing air with water, or freezing water do not relate to steam production and are not part of the operational mechanics of a boiler.