Which type of clouds is indicative of unstable air conditions?

Cumuliform clouds are indeed indicative of unstable air conditions. These clouds, such as cumulus and cumulonimbus, typically form in an environment where warm, moist air rises rapidly. This upward motion is a characteristic of instability, as it allows the warm air to rise and cool, leading to the development of these vertical cloud structures.

In unstable conditions, the air temperature decreases more rapidly with height than in stable conditions, encouraging continuous vertical movement. This results in clouds that have significant vertical development and often indicate active weather phenomena, including thunderstorms when sufficient moisture and atmospheric lift are present.

Other cloud types like stratus are representative of stable air where the atmosphere is generally calm, leading to layered cloud formations without much vertical growth. Nimbostratus clouds, while associated with precipitation, typically form in stable conditions with widespread overcast skies rather than significant vertical development. Cirrocumulus clouds, being high-altitude and often composed of ice crystals, are generally found in stable air and do not reflect unstable conditions in the atmosphere.