Internal energy is a function of a state because change in internal energy:

Explanation

The correct answer is that internal energy does not depend on path. This is because internal energy is a state function, which means it is determined solely by the state of the system, such as temperature and pressure, and not by the path taken to reach that state. Unlike path-dependent quantities like work and heat, state functions are independent of the process. Option B is incorrect because while isothermal processes involve constant temperature, they do not define internal energy itself as a state function. Option C is incorrect because it suggests a path dependency, which is not true for state functions. Option D is incorrect because adiabatic processes describe how internal energy changes (through work) but do not define it as a state function.