Sodium Chloride & Electricity
 

A question that i'm stuck with is ' explain why sodium chloride conducts electricity in the molten state but not when it's a solid'. please could you help me!

also, what are 2 properties of metal which are caused by the displaced sea of electrons that is metallic bonding?

This is really easy. To conduct electricity, you need FREELY MOVING particles with CHARGE. Not anything else, but moving particles with charge. In solid state between the particles of salt there are gaps, that you probably don't see, but electricity can't "jump", only if it has high current. So if it is melted, you have now moving particles with charge, that can conduct.

Metals with displaced sea of electrons because of the displacement can conduct electricity in solid state, because electrons have charge, relatively -1, and they move freely. Also, because of the big cloud electrons they tend to absorb light, or, reflect it in a strange way, this is why some of them are reflective, and most of them are greyish-black colored(absence of light is called black :D)

The sodium ions and chloride ions in the solid are tightly held in a lattice/crystal structure. To carry electricity they need to be able to move along in a particular direction. They can do this in the molten state.

when NaCl is put into water it dissociates into its ionic forms, Na+ and Cl-. these ions allows the flow of electricity on your solution. thus conductivity occurs.

Note/ The question wasn't about dissolving in water, it was about molten NaCl. :)

Metals are different from ionic substances because, even when metals are solid, they still have free electrons floating around to carry electricity.

In ionic solids, electrons aren't free to move around. In ionic solids, its the whole atom (more correctly the whole ion, which is an atom minus or plus an electron or two) that needs to move to carry electricity and this can only happen if the ionic solid is melted, or like KathChem said, dissolived in a liquid.