Question

what are the essential factors for the formation of ionic bond

Answer 1

the essential factors for the formation of ionic bond :
the ease formation cation and anion
ionisation enthalphy of cation must be small in amount
electron gain enthalphy of anion must be large

Answer 2

Cations and anions must have electronegativity difference and IE of cation should be small and EGE of anion must be large enough.