Step-by-step explanation:
Option C, 2 Celsius degrees per 1000 meters, is stable for unsaturated air parcels.
The lapse rate refers to the rate at which the temperature of the air changes with height. The standard lapse rate is approximately 6.5 Celsius degrees per 1000 meters for the lower atmosphere. However, this value can vary depending on the moisture content of the air.
In unsaturated air parcels, the lapse rate is generally more stable and closer to 2 Celsius degrees per 1000 meters. This is because unsaturated air parcels cool at a slower rate due to the release of latent heat during the process of evaporation.
Therefore, option C, 2 Celsius degrees per 1000 meters, is the correct answer.