Compound A’ and aluminium are used to join railway tracks,

Railway trakcs as we all know, are made up of iron. This means that the compound A is an oxide of iron (Fe2CO3). It is reduced by aluminium by

thermit reaction with aluminium.

$\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+2 \mathrm{Al}(s) \longrightarrow \mathrm{Al}_{2} \mathrm{O}_{3}(s)+2 \mathrm{Fe}(s)+$ heat.

The reaction is highly exothermic and as a result, iron is in molten state and can weld the broken railway tracks. The process is also called

aluminothermie reduction or thermit process.