(i). Alkali metals have the lowest ionization enthalpy in each period.
(ii). Within the group, as we go down, the ionization enthalpies of alkali metals decreases due to the increase in atomic size.
(iii). In large atoms, the valence electrons are loosely held by the nucleus and arc easily lost, leading them to have low ionization enthalpy and acquiring stable noble gas configuration.
(iv). On moving down the group, the atomic size increases and the number of inner shells also increases, which in turn increases the magnitude of screening effect. So. the ionization enthalpies decreases down the group.
