Conductors and non-conductors 

( a ) Non - conductor or insulator :

Substances which do not allow electric current to pass through them are called non-conductors or insulators.examples - pure water, ice, glass, rubber etc.

( b ) Conductor : 

Substances which allow electric current to flow through them are called conductors. Examples -Metals, Aqueous solution of acids, bases and salts, fused salts and impure water etc.

Conductors are of two types :

(i) Metallic conductors (ii) Electrolytic conductors or electrolytes.

( i ) Metallic conductors :

The conductors which conduct electric current by movement of electrons without undergoing any chemical change are known as metallic conductors.Metals (Cu,Ag,Fe,Al etc), non metals (graphite) and various alloys and minerals are examples.

(i i) Electrolytic conductors :

Those substances whose water solution conducts the electric current and which are decomposed by the passage of current are called electrolytes. In this case, conduction takes place by movement of ions. electrolytes also conduct electricity in fused state and undergo decomposition by passage the electric current. Substances whose aqueous solution does not conduct electric current are called non-electrolytes.

They do not conduct electricity in the fused state also. Solutions of cane suger, glycerine, glucose, urea etc. are the examples of non electrolytes.

Strong electrolyte :

Electrolytes which are completely ionized in aqueous solution or in their molten state, are called strong electrolytes. Example – all salts, strong acid and strong base

Weak electrolyte :

Electrolytes which are not completely ionized in aqueous solution or in their molten state, are called weak electrolytes. Examples :- All carbonic acids (except sulphonic acid), CH3COOH, HCN, NH3, amine, etc.