The increasing order of reactivity among group 1 elements is `Li< Na< K< Rb < Cs` whereas in group 17 `F> Cl> Br> I` Explain.

Explanation

The elements of group I have only one electron in their respective valence shells and thus have a strong tendency to lose this electron. The tendency to lose electrons in turn, depends upon the ionization enthalpy. Since the ionization enthalpy decreases down the group therefore, the reactivity of group 1 elements increases in the same order LiltNaltKltRbltCs. In contrast. the elements of group 17 have seven electrons in their respective valence shells and thus have strong tendency to accept one more electron to make stable configuration. It is linked with electron gain enthalpy and electronegativity. Since both of them decreases down the group, the reactivity also decreases.