S-block elements, which include groups 1 and 2 of the periodic table, are characterized by their large atomic radii and low ionization energies. These properties make them highly electropositive, meaning they readily lose electrons. As a result, they act as reducing agents by donating electrons to other elements, thereby reducing them. Option B is correct because it reflects this behavior. Option A is incorrect because oxidizing agents gain electrons, which is not typical of s-block elements. Option C is incorrect because s-block elements do indeed function as reducing agents. Option D is incorrect because s-block elements do not act as both oxidizing and reducing agents; they primarily serve as reducing agents.

Option A is incorrect because oxidizing agents are substances that gain electrons in the process of oxidizing another species. S-block elements, being highly electropositive, prefer to lose electrons rather than gain them.

Option B is correct. S-block elements, such as alkali metals, have large atomic radii and low ionization energies, making it easy for them to lose electrons. This loss of electrons allows them to reduce other substances, acting as reducing agents.

Option C is incorrect. S-block elements are known for their reducing capabilities due to their tendency to lose electrons and cannot be classified as neither.

Option D is incorrect. S-block elements cannot act as both oxidizing and reducing agents since they predominantly lose electrons and act as reducing agents.