Which condition is most likely to result in the formation of fog?

The formation of fog is most likely to occur when warm moist air comes into contact with a much colder surface, such as cold water. This is because as warm air rises and meets the cooler surface, it cools down and loses its ability to hold moisture, resulting in condensation. The water vapor condenses into tiny droplets, creating fog.

When warm moist air blows over cold water, the temperature differential between the air and water facilitates this condensation process effectively, leading to dense fog conditions. This phenomenon is especially common in coastal areas where warm winds from the land move over the cooler waters of the ocean.

In contrast, while cold air settling over warm land could create some instability, it does not necessarily lead to fog but can lead to other weather phenomena instead. Heavy rain following a drought might lead to increased humidity, but the specific conditions for fog formation are not inherent in this scenario. Additionally, a high-pressure system typically stabilizes the atmosphere and can lead to clear weather instead of fog.