$word_{count}$: 200

Combined contribution: ~3% of JEE Main. Priority areas: (1) Hardy-Schulze rule — rank coagulating power by ion valence. Know charges on common colloids (As2S3 negative, Fe(OH)3 positive). (2) Freundlich isotherm log plot — find k and 1/n from graph. (3) Physisorption vs chemisorption comparison — temperature/pressure effects, enthalpy, layer type. (4) Z vs P plot — identify Z < 1 and Z > 1 regions, behaviour of H2/He. (5) van der Waals constants — a for liquefaction ease, b for molecular size. (6) Molecular speeds — ratio $u_{mp}$:$u_{avg}$:$u_{rms}$ = 1:1.128:1.224. (7) Catalyst properties — does NOT change $K_{eq}$. Common mistakes: (a) Confusing adsorption with absorption. (b) Hardy-Schulze: using same-sign ion instead of opposite. (c) Forgetting H2 and He have Z > 1 at all pressures. (d) Confusing $T_B$ (Boyle) with $T_c$ (critical) with $T_i$ (inversion). (e) Saying catalyst changes equilibrium. Quick recall: $T_i$ = 2$T_B$, $T_B$ = 27$T_c$/8. Higher 'a' = easier liquefaction = lower $T_c$... No: higher 'a' = higher $T_c$ (more attraction).