Vapor–gas systems: the gravimetric (by-weight) composition of a vapor-saturated gas depends on what variables? Pick what it is independent of.

Introduction / Context:
When a non-condensable gas is saturated with a condensable vapor (e.g., air saturated with water vapor), composition can be expressed on a mass basis (gravimetric humidity). Engineers must know which variables control this composition to do humidification, drying, and absorber design correctly.

Given Data / Assumptions:

• At saturation, the vapor partial pressure equals its saturation pressure at the system temperature.
• Ideal-gas approximation for the gas–vapor mixture in many calculations.
• Gravimetric composition typically expressed as mass of vapor per mass of dry gas.

Concept / Approach:
For a given liquid, saturation pressure p_sat depends strongly on temperature (Clausius–Clapeyron behavior), so composition depends on temperature. The total pressure matters because y_vapor = p_sat / P_total under ideal assumptions, which influences the mass ratio via y/(1 − y). The nature of the non-condensable gas influences the gravimetric ratio through its molecular weight in converting mole fractions to mass ratios; the liquid’s nature sets p_sat(T). Therefore, gravimetric composition is not independent of any of the listed variables; it depends on all of them.

Step-by-Step Solution:

Verification / Alternative check:
Psychrometric relations confirm that humidity ratio w varies with both temperature and pressure and depends on gas and vapor molecular weights.

Why Other Options Are Wrong:

• (a), (b), (c) each affect w directly or indirectly; selecting any implies false independence.
• (e) “gas molecular weight only” ignores other determinants and is incomplete.

Common Pitfalls:
Confusing mole-based independence (mole fraction of vapor at saturation is independent of the gas identity) with mass-based independence; gravimetric measures are sensitive to molecular weights.

Final Answer:
none of these