Ответ:

1) The chemical activity of alkali metals is closely related to the structure of their atoms. Alkali metals have a single valence electron in their outermost energy level, which is not strongly attracted to the positively charged nucleus. This makes it relatively easy for alkali metals to lose their valence electron and form positive ions, which gives them their high chemical reactivity.

2) The reducing properties of the elements of the II groups of the main subgroups generally increase as you move down a group or period. This is because the elements in these groups have a lower electronegativity and a higher ionization energy, which makes it easier for them to donate electrons and reduce other substances.

3) The reducing ability of alkali metals in an aqueous medium does not always correspond to their activity in air because the presence of water can affect their chemical reactivity. For example, the hydroxide ions present in an aqueous solution can react with alkali metal ions to form hydroxides, which may reduce their ability to react with other substances.

4) Among the alkaline earth metal hydroxides, barium hydroxide is the weakest base and strontium hydroxide is the strongest base. This is because the smaller the ionic radius of the metal ion, the stronger the base. Since barium has a larger ionic radius than strontium, it forms a weaker base.