A vapor can be condensed effectively at a high temperature if its pressure is?

The effectiveness of condensing a vapor at a high temperature is influenced significantly by the vapor's pressure. When the pressure of the vapor is high enough, it raises the saturation temperature. This means that at a specific pressure, the vapor can exist at a higher temperature before it transitions to a liquid state. Consequently, under high pressure conditions, the condensed vapor can be reliably achieved even when temperatures are elevated.

In practical applications, such as refrigeration and air conditioning, operating under higher pressures facilitates the condensation of refrigerants that may otherwise remain gaseous at ambient temperatures. This principle is crucial for ensuring that the cooling cycle runs efficiently, with the condensed liquid refrigerant being effectively returned to the evaporator.

The other options relate to conditions that are less favorable for effective condensation at high temperatures. For instance, a low pressure would lower the saturation point, making it difficult for the vapor to condense at higher temperatures. Atmospheric pressure may allow for condensation, but it typically does not guarantee effectiveness at higher temperatures due to the limitations in saturation temperature. If pressure is variable, it could lead to inconsistent operations that may hinder the condensation process. Therefore, high enough pressure is the key to successfully condensing vapor at elevated temperatures.