Here's why:

* Molecular compounds are formed by the sharing of electrons between atoms (covalent bonds).

* Water is a polar solvent, meaning it has a positive and negative end due to uneven sharing of electrons in the O-H bonds.

* Some molecular compounds dissolve in water because the polar water molecules can surround and interact with the molecules of the compound, pulling them apart.

* Not all molecular compounds dissolve in water. The ability of a compound to dissolve depends on the strength of the attraction between the water molecules and the molecules of the compound.

* Some molecular compounds that dissolve in water can conduct electricity because they ionize in solution. This means they break apart into charged ions (cations and anions). These ions are free to move and carry an electric current.

Examples:

* Sugar (sucrose) is a molecular compound that dissolves in water but does not conduct electricity because it doesn't ionize.

* Hydrochloric acid (HCl) is a molecular compound that dissolves in water and conducts electricity because it ionizes into H+ and Cl- ions.

Key takeaway: Whether a molecular compound conducts electricity in water depends on whether it ionizes, not just on whether it dissolves.