Acetone and sodium chloride both have similiar mass. Explain why their other properties differ.

Acetone: C3H6O, melting point = −94°C, liquid at room temperature, low electrical conductivity

Sodium chloride: NaCl, melting point = 801°C, solid at room temperature, high electrical conductivity

It is the type of compounds that they are, and the molecular interactions those compounds have.  Acetone is a nonpolar covalent bonded molecule.  The forces that this compound if greatly dependent on the molecular mass.  These type of compounds generally have only van der Waals and London forces acting on them.  Both of these forces are VERY weak and allows for a VERY low melting point.  Not to mention that nonpolar molecules do not conduct electricity.

Compare that to sodium chloride, an ionic compound.  Ionic compounds are all VERY good conductors of electricity.  The high melting point is from the electrical forces that are interacting with the sodium and chloride elements.  The movement of the atoms need to overcome that strong force so the compound can melt.

it is b that is the answer.