Concept:Impurities disrupt the regular crystal lattice of a pure metal and lower its melting point.Explanation:Pure iron has a regular lattice and a fixed, high melting point.When impurities like carbon and sulphur are present, they distort the lattice, so less heat is needed to break it.This lowers the melting point of iron rather than increasing it.Impurities do not make iron malleable or ductile; in fact, they can make it harder and more brittle.Answer:D. lower its melting point