What is the entropy change when two gases mix isothermally?
Mixing of gases increases disorder due to increased randomness, so Δ S > 0. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Chemistry Textbook for Class XI and XII, Chapter: Some Basic Concepts, Structure of Atom and Periodicity, Topic: Mole concept, atomic models and periodic trends.