Weak electrolytes. Those electrolytes which do not ionize completely in an aqueous solution or in a molten state are called weak electrolytes, e.g., H2CO3 (carbonic acid), H3BO3 (boric acid), HCN (hydrocyanic acid), CH3COOH (acetic acid), CHCl2COOH (dichloroacetic acid), HgCl2 (mercuric chloride), etc. They have a small degree of ionization.
Strong electrolytes. Those electrolytes which dissociate completely into ions are called strong electrolytes, e.g., NaCl, HCl, NaOH, etc.
Degree of ionisation. It is the ratio of number of ions produced to the total number of molecules of electrolyte.