(Steel : Utensils) , (Bronze : Statue) , (Duralumin : Aircraft) , (Iron : Rails)
Option:
Justification: In all other pairs, first is the alloy used to make the second. (Iron is not an alloy, but a metal.)

(Steel : Utensils) , (Bronze : Statue) , (Duralumin : Aircraft) , (Iron : Rails)
Justification: In all other pairs, first is the alloy used to make the second. (Iron is not an alloy, but a metal.)