Which of the following is true about the characteristics of radiation fog?

The correct answer highlights a critical characteristic of radiation fog. This type of fog is formed when the ground loses heat through radiation on a clear night, causing the temperature of the air near the surface to cool and reach the dew point. This cooling usually occurs in low-lying areas where the air can become stable and stagnant, leading to higher humidity levels near the surface, which favors the development of fog.

The conditions for radiation fog are most optimal during clear nights when there are few clouds to trap heat, allowing the ground temperature to drop significantly. As such, low-lying areas are particularly susceptible to this phenomenon since cold air sinks and accumulates in these regions, making them more likely to cool quickly and facilitate fog formation.

In contrast, while radiation fog can indeed occur in various regions, it is not necessarily confined to mountainous areas, nor is it exclusively a winter phenomenon. It can also occur in the spring and fall as well, making it inaccurate to assert that it can only form during winter months or that it is more common specifically in mountainous regions. Therefore, the characteristics of radiation fog align perfectly with its tendency to develop in low-lying areas on clear nights, confirming the accuracy of the correct answer.