This document discusses ideal and non-ideal gases, focusing on how they behave according to the combined gas law and Van der Waals equation. It also covers vapour pressure and how Raoult's law describes the relationship between vapour pressure and composition in ideal solutions. Non-ideal behaviour is examined for mixtures like hydrocarbon propellants, anaesthetic agents, and drug-solvent combinations, which can show positive or negative deviations from Raoult's law due to intermolecular interactions.