Final answer:
The temperature inside an air parcel relative to the surrounding air, along with the Environmental Lapse Rate (ELR), determines if the air parcel will rise (unstable) or not. Warmer air inside a parcel compared to cooler air outside makes it buoyant, causing it to rise.
Step-by-step explanation:
The determinant of whether a parcel of air will rise (unstable) or not rise (stable) is C) The temperature inside the parcel compared to the temperature outside the parcel, and the Environmental Lapse Rate (ELR). If the temperature inside the parcel is warmer than the surrounding air, it will rise, because warmer air is less dense than cooler air, creating buoyancy. The ELR informs us about the rate at which the air temperature decreases with an increase in elevation within the environment. When the parcel's temperature decreases more slowly with altitude than the ELR, it remains warmer and less dense than the surrounding air, making it unstable and likely to rise. This concept also explains the lifting capacity of a hot air balloon, which is based on the difference in density between the hotter air inside the balloon and the colder air outside.