Final answer:
Two air masses are likely to stay separated primarily due to density differences, caused by variations in temperature and moisture content, with hot air being less dense than cold air.
C is correct
Step-by-step explanation:
The reason why two air masses are likely to stay separated from one another is primarily due to density differences, which is the correct answer (C). Air masses have different characteristics based on their temperature and moisture content, which directly affect their density.
Hot air is less dense than cold air, leading to a natural separation between air masses of varying temperatures. This concept is further supported by the fact that warm air can hold more moisture than cold air, indicating that moisture differences also contribute to the formation of distinct air masses. However, density is the principal factor that keeps them from mixing easily, as it leads to stratification in the atmosphere.