The correct option is A Low ionisation enthalpy of one atom and high electron affinity of the other atom
The formation of electrovalent bond depends on two factors: Ionization enthalpy (IE) & Electron affinity (EA).
Lesser the value of ionization enthalpy, greater is the tendency of the atom to form a cation by removal of electrons.
Similarly, higher the value of electron affinity, more is the tendency of the atom to form an anion by accepting electrons.
Hence, for any electrovalent bond formation one atom should have low IE and other atom must have high EA.