What are any two independent properties that can be used to obtain the remaining properties?

• A. Two independent properties of the system
• B. Saturated properties
• C. Vapor pressure and temperature
• D. Density and viscosity

Answer: (A)

For a simple compressible system, the state is defined by two independent properties. Knowing two independent properties allows you to use the equation of state and property correlations to compute all other properties such as pressure, temperature, density, internal energy, enthalpy, and entropy. This is why the statement “two independent properties of the system” best fits the idea: independence means the properties aren’t fixed by a single constraint, so once you have two, the rest follow from the relationships between properties.

Saturated properties, and pairs like vapor pressure and temperature on the saturation line, are tied together by a boundary relation, so they aren’t independent inputs. Density and viscosity are just two properties and, without a specific state equation or additional independent input, don’t by themselves uniquely determine the entire state.