The formation of electrovalent bond is an example of:

1. Oxidation reaction
2. Reduction reaction
3. Displacement reaction
4. Redox reaction

Redox reaction

Reason — In the formation of an electrovalent bond, the transfer of electron(s) is involved. The electropositive atom loses electrons and undergoes oxidation, while the electronegative atom gains electrons and undergoes reduction. This is known as redox reaction.
Oxidation reaction involves loss of electrons only. Reduction reaction involves gain of electrons only. In displacement reaction one element replaces another from a compound.