What best describes unstable air?

Unstable air is characterized by the tendency to rise continuously once it has been lifted. When air becomes heated, it becomes less dense than the cooler air surrounding it, causing it to rise. This process leads to the development of convection currents, which are important in producing various weather phenomena, including thunderstorms. An unstable atmosphere allows for vigorous vertical development of air parcels, often leading to the formation of clouds and precipitation.

In contrast, cooler and denser air tends to remain at its altitude or sink. When air remains at its initial altitude or is forced downward while separating from warmer air, it does not exhibit the characteristics of instability that define active weather conditions. Thus, the defining quality of unstable air is its ability to rise persistently, which is correctly represented by the selected response.