Saturated steam exists at which of the following conditions?

Saturated steam exists at corresponding temperature and pressure, which means that for a given pressure, there is a specific temperature at which water can coexist with steam. At this point, the steam is at saturation, meaning it can exist in both liquid and vapor phases simultaneously. This relationship is defined by the steam tables, where each pressure correlates with a specific saturation temperature.

When steam is saturated, any increase in temperature will lead to superheating if pressure remains constant, or condensation if pressure decreases. Conversely, if the pressure increases at constant temperature, the steam could transition to a superheated state. Thus, the concept of corresponding temperature and pressure is essential to understanding the behavior of saturated steam, making this the key characteristic of its existence.

In the context of the other options, they describe conditions that don't accurately reflect the thermodynamic relationship of saturation. Fixed temperature and variable pressure do not specify the necessary correlation needed for saturation. Constant temperature regardless of pressure describes a scenario that is not consistent with the behavior of steam at saturation. Lastly, variable temperature and fixed pressure cannot ensure that the conditions for saturation are maintained, as saturation is inherently linked to specific temperature-pressure pairs.