There is a general tendency for liquids to conduct electricity better than solids due to

There is a general tendency for liquid to conduct electricity better than solids due to free ions.

Explanation:

There is a general tendency for liquid to conduct electricity better than solids due to free ions.

Take an example of aqueous NaCl and solid NaCl.  When Nacl is dissolved in water then it will get dissociated in to ions. This state of NaCl is called aqueous state of the Nacl. In this state , the ions are free to conduct electricity.

Solid NaCl does not have free ions to conduct electricity.

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.