Option 1: Neutrally stable means that the temperature does not change with height. In this case, the ambient lapse rate is not stable.

Option 2: Hyper-adiabatic means that the temperature decreases more rapidly with height than the average adiabatic lapse rate. This would create an unstable atmosphere, not a stable one.

Option 3: Sub-adiabatic means that the temperature decreases slower with height than the average adiabatic lapse rate. This creates a stable atmosphere, where air parcels near the surface are cooler than those higher up.

Option 4: Super-adiabatic means that the temperature decreases faster with height than the average adiabatic lapse rate. This would also create an unstable atmosphere.

The correct answer, option 3, indicates that when the ambient lapse rate is sub-adiabatic, the air is stable.