In the joining of railway tracks, iron oxide is made to react with

The correct answer is A, Aluminium. Railway tracks are joined by the thermite process, in which aluminium powder reduces iron oxide to molten iron. The reaction is Fe₂O₃ + 2Al → 2Fe + Al₂O₃. It is a displacement reaction: aluminium is more reactive than iron, so it takes the oxygen away from iron oxide. The reaction gives out so much heat, reaching well over 2,000 °C, that the iron produced is liquid; it is poured into a mould placed around the gap between two rails and welds them together. Because the mixture carries its own heat source, the method works on site without electricity, which is why it is used on railway lines and for repairing cracked machine parts. Option B is wrong because zinc is used mainly to galvanise iron against rusting. Option C is wrong because copper is less reactive than iron and cannot displace it from its oxide. Option D is wrong because tin is also less reactive than aluminium and is used for coating cans and in solder. Exam tip: thermite welding = iron oxide + aluminium powder, a highly exothermic displacement reaction.