In which branch of thermodynamics would one primarily study the properties of matter in states of flux?

The correct choice is to study the properties of matter in states of flux in Non-Equilibrium Thermodynamics. This branch focuses on systems that are not in a state of equilibrium, meaning that there are gradients of temperature, pressure, or concentration, leading to flows and changes over time. Non-Equilibrium Thermodynamics examines how systems evolve toward equilibrium and the processes and phenomena that occur during this evolution.

The importance of this field lies in its application to real-world scenarios, where many systems, such as biological processes, chemical reactions, and material transformations, are constantly changing and not in a stable state. Understanding these dynamic properties is essential for accurately predicting how systems will behave under varying conditions.

In contrast, Equilibrium Thermodynamics deals with systems in a stable state where all macroscopic properties are constant over time. Classical Thermodynamics often includes aspects of equilibrium and non-equilibrium scenarios but does not specifically focus on states of flux. Statistical Thermodynamics provides a microscopic foundation for understanding thermodynamic properties based on statistical distributions of particles, which applies to both equilibrium and non-equilibrium states but does not explicitly center on the study of dynamics in a state of flux. Therefore, Non-Equilibrium Thermodynamics is the appropriate branch for understanding how matter behaves in transitional states