Concept:Thermosetting polymers set permanently on heating and cannot be remoulded, whereas thermoplastics soften on heating and can be reshaped.Explanation:Bakelite is a cross-linked polymer that hardens irreversibly when heated.It cannot be softened or reshaped once set.Nylon, polypropene, and polystyrene are all thermoplastics.They soften when heated and can be reshaped repeatedly.Therefore, the thermosetting polymer among the options is Bakelite.Answer:A. Bakelite