The pair that would react most easily with each other is:
an element with a high electronegativity and an element with a single valence electron.
This combination typically leads to reactions where the highly electronegative element can attract and gain the single valence electron from the other element, leading to the formation of an ionic bond. Elements with a single valence electron (like alkali metals) readily lose that electron to achieve a full shell, while highly electronegative elements (like halogens) readily accept electrons to complete their outer electron shells.