How the reducing properties change in the series Li-Na-K-Rb which element has the smallest radius.

Reducing properties – the ability to donate electrons, they are most pronounced in chemical elements related to metals. The activity of metals belonging to one group, the main subgroup, increases from top to bottom due to the fact that the number of energy layers increases, and, therefore, the radius of the atoms, together with the reducing ability. Lithium, sodium, potassium and rubidium belong to the chemical elements of group I of the main subgroup. This means that the reducing properties in the series Li – Na – K – Rb increase. Lithium (Li) has the smallest atomic radius of the above elements.