The three components of atmospheric density are

• A. Speed, Temperature, Humidity
• B. Pressure, Humidity, Viscosity
• C. Temperature, Pressure, Humidity
• D. Altitude, Temperature, Density

Answer: (C)

Air density is the mass of air per unit volume, and it’s determined by the thermodynamic state and composition of the air: temperature, pressure, and the amount of water vapor present (humidity).

If you raise the temperature while holding pressure the same, the air expands and becomes less dense. If you raise the pressure at the same temperature, the air is squeezed tighter and becomes more dense. Humidity matters because water vapor has a lower molecular weight than the main components of air. Increasing humidity means replacing some heavier nitrogen and oxygen with lighter water vapor, which lowers the overall density of the air at the same temperature and pressure.

So the three factors that define atmospheric density are temperature, pressure, and humidity. Choices that include speed or viscosity don’t set density, and altitude is a condition that affects density but is not a direct component that defines it.