Sulphur shows extensive allotropy — most stable is rhombic S8 (crown-shaped ring). Oxidation states: -2, +2, +4, +6. SO2: Bent molecule, acidic (SO2 + H2O → H2SO3), acts as reducing agent (SO2 + Cl2 → SO2Cl2) but also as oxidising agent with strong reductants (SO2 + 2H2S → 3S + 2H2O). Bleaches by reduction (temporary, colour returns). H2SO4: Strong acid, powerful dehydrating agent (chars sugar), oxidising agent when hot concentrated (reacts with Cu, C). Contact process: S → SO2 → SO3 (V2O5 catalyst) → H2S2O7 → H2SO4. SF6: Exists because S has d-orbitals. Octahedral, highly stable, used as gaseous insulator. OF6 doesn't exist (O has no d-orbitals).