Rusting of iron is an electrochemical process. At anodic spots: Fe -> Fe2+ + 2e- (iron dissolves). At cathodic spots: O2 + 2H2O + 4e- -> 4OH- $\frac{oxygen reduction in neutral}{basic conditions}$. Fe2+ + 2OH- -> Fe(OH)2, which is further oxidised to Fe2O3.xH2O (rust). Conditions: moisture + oxygen + an electrolyte (salt accelerates). Prevention methods: (1) Barrier coating (paint, oil, grease). (2) Galvanisation (Zn coating — Zn is sacrificial anode). (3) Cathodic protection (connecting to a more reactive metal like Mg). (4) Alloying (stainless steel contains Cr, which forms protective Cr2O3 layer). (5) Sacrificial anode method: attaching blocks of Zn or Mg to iron structures (ships, pipelines).