Final answer:
Standard conditions at sea level are 29.92 inches of mercury (Hg) and 15°C, which correlate to the atmospheric pressure and temperature at which air has a density of approximately 1.29 kg/m³ at sea level.
Step-by-step explanation:
Density altitude refers to a theoretical air density that exists under standard conditions at a given altitude. The question asks about what standard conditions at sea level are.
This is because standard atmospheric pressure at sea level is often equated to the pressure exerted by a column of mercury that is about 760 mm (29.92 inches) high. The corresponding temperature associated with this standard pressure is 15°C.
The density of air at sea level is approximately 1.29 kg/m³ under these standard conditions, which is much higher than the average density of air throughout the atmosphere up to 120 km. Since air is compressible, its density is highest near the Earth's surface and decreases with altitude.
This concept is crucial when discussing density altitude, as it impacts weather, flight conditions, and engine performance.
The correct response is 1) 29.92 in. of Hg (inches of mercury) and 15°C.