Answer: B. The molecules move faster and become less dense
Step-by-step explanation:
Liquid is the state of matter in which particles are less tightly bound as compared to solids as they have weak inter molecular forces as compared to solids.
Thus when a solid is heated, the molecules start moving in random motion due to an increase in the kinetic energy. The molecules move apart as the forces will be weak and thus less molecules will be present per unit volume. Thus it will become less dense.