Why is sodium the reducing agent in the formation of sodium chloride?

In the formation of sodium chloride, sodium acts as the reducing agent because it furnishes, or donates, electrons to chlorine atoms.1

In this oxidation-reduction reaction, each sodium atom loses an electron to become a positively charged sodium ion ($N{a}^{+}$), a process defined as oxidation. Because the sodium atom provides the electrons that are subsequently gained by the chlorine atoms—which are thereby reduced—sodium is classified as the reducing agent. Metals are generally considered the most common reducing agents because they have a natural tendency to lose electrons when reacting with nonmetals.1