PV = nRT, is the a. equation of state of an ideal gas

b. theorem of equipartition of energy

c. second law of thermodynamics

Ideal gas law:

PV = nRT

P = pressure, V = volume, n = # of moles, R = gas constant, T = temperature

Equipartition theorem:

Each degree of freedom that a molecule has adds 0.5kT to its total internal energy where k = Boltzmann's constant and T = temperature

2nd law of thermodynamics:

A set of governing principles that restrict the direction of net heat flow (always hot to cold, heat engines are never 100% efficient, entropy always tends to increase, etc)

Clearly the answer is Choice A