For a monatomic ideal gas undergoing an isothermal process, the total internal energy is U = (3/2)NkT, where N is the number of atoms. Since T does not change during this process, what does the source conclude about ΔU and about the relationship between Q and W?

1. The internal energy of a monatomic ideal gas depends only on N, k and T, with no other variable involved. 2. Since T is held fixed throughout an isothermal process and N and k never change, U itself does not change, so ΔU = 0. 3. The first law states ΔU = Q - W, so setting ΔU to zero gives Q = W directly. 4. This rules out options A and B, which both assign ΔU a nonzero value despite temperature staying constant. 5. ΔU is perfectly well defined here, it is simply zero, so option C's claim that no comparison is possible is incorrect. _Source: OpenStax College Physics (CC BY 4.0), Ch 15 "Thermodynamics", section 15.2 The First Law of Thermodynamics and Some Simple Processes_