Define strong and weak electrolytes

Depending upon the extent or degree of ionization, the electrolytes are divided into two types:
Strong electrolytes and Weak electrolytes

Strong electrolytes:
The substances, in aqueous which ionize almost completely into ions are known as strong electrolytes. The unionized molecules are present to such a small extent that it is not of any significance to study the ionization constant of strong electrolytes. For example: HCl, H₂SO₄, HNO₃, NaOH, KOH, NaCl etc. are strong electrolytes.

The equation which involves the ionization of strong electrolytes is represented with only single headed arrow directed to the right. For example,
HCl + H₂O ———-> H₃O⁺ + Cl^–

HNO₃₂O ——-> H₃O⁺ + NO₃^–

Weak electrolytes:
The substances, in aqueous which ionize to a small extent into ions are known as weak electrolytes. For example: CH₃COOH, NH₄) OH, HCN etc. are weak electrolytes.

In this case, the molecules are in equilibrium with their ions. The equation which involves the ionization of weak electrolytes is represented with double headed arrows. For example,
CH₃COOH + H₂O ⇌ H₃O⁺ + CH₃COO^–
NH₃ + H₂O ⇌ NH₄⁺ + OH^–