Which description fits the characteristics of an unstable atmosphere?

In meteorology, an unstable atmosphere is characterized by conditions that promote vertical motion and turbulence. A warm, humid air mass is particularly conducive to instability because warm air tends to rise. When air is heated from below, it expands and becomes less dense compared to the surrounding cooler air. As a result, the warm, humid air will rise, leading to the formation of clouds and potentially convective weather phenomena such as thunderstorms.

When the air is humid, it also contains moisture that can contribute to cumulus cloud formation, further indicating instability. In contrast, cool, dry air typically leads to a more stable atmosphere where vertical motion is suppressed, resulting in less cloud formation and calmer weather conditions. Therefore, the presence of a warm, humid air mass aligns with conditions that promote instability and active weather patterns.