Question

Copper shows electrical conductance in solid as well as in molten state whereas copper chloride shows electrical conductance only in the molten state. Give reason.

Answer 1

Conductivity of metals or ionic compounds depend upon the presence of free electrons or free ions. The conductivity of the ionic compound depends upon the ionization of that compound in aqueous solution.

Complete answer:
Conductivity is the ability to conduct electricity which depends upon the presence of free electrons as well as free ions.
The electrons present in the outermost shell of the metal are very loosely bound because the nucleus has very little attraction on the outermost shell electrons. Thus, on applying heat the electrons of metal become mobile and conduct electricity. So, the copper metal conducts electricity in solid as well as in the molten state.
In ionic compounds, such as copper chloride $CuCl_2$ the free electrons are not present. Electrons are bound in bonds by strong electrostatic forces. So, copper chloride does not conduct electricity in solid-state. On dissolving in water, the copper chloride dissociates into a copper ion and chloride ion and these ions conduct electricity.
Therefore the reason for the conductivity of copper in solid as well as in molten state is the presence of free electrons and the reason for the conductivity of the copper chloride in molten state only is the production of ions in the molten state.

Note: The conductivity of metal is due to the free electrons which present in both the solid and molten state whereas the conductivity of the ionic compound is due to ions which are present in solid state but become free only in molten state. Free electrons increase the conductivity of metal increases. The small ions become more hydrated in aqueous solution, so the conductivity decreases on decreasing the size of the ion.