Why basicity increases in group 1?

Basicity increases in Group 1 (alkali metals) due to the increasing atomic size and decreasing ionization energy as you move down the group. Larger atomic radii result in a weaker hold on the outermost electron, making it easier for these elements to lose that electron and form hydroxides. Consequently, the resulting hydroxides become more soluble and stronger bases as you go down the group, leading to increased basicity.