Give reasons :
i) lonic compounds in solid state do not conduet electricity, whereas in molten state are good conductors of electricity.
(ii) ii) Silver articles when exposed to air gradually turn blackish.
ii) Chenmical reaction does not take place when copper is added to iron sulphate solution.

Explanation

(i) In the solid state ionic compounds do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure.
In solid state, they are hard because of the strong force of attraction between the positive and negative ions.
In molten state, electrostatic forces of attraction between the oppositely charged ions are overcome due to the heat.
thus the ions nnove freely and conduct electricity. (ii) Silver reaucts with sulphur in the air to fornm a coating of silver sulphide.
Reactivity of copper is less than that of iron.