CAIE IGCSE Chemistry 0620/42 May/June 2023 – Model Answers: worked solutions on periodicity/halogens & isotopes, Contact Process (equilibrium/conditions), acids–bases/salts (amphoteric oxides, pH), and titration calculations.  Includes organics (photochemical substitution, polymers, esters) with clear reasoning, balanced equations, and exam-style explanations—ideal for self-marking and fast revision.