This is due to the fact that all of these elements have only one electron in their outer shell. As a result, the fastest way for them to obtain a full outer shell is to simply lose an electron. read more
Group one elements are strong reducing agents because they have one valence electron in their outermost shell therefore they are loosely bound by the nucleus causing them to increase in their atomic size and as a result their ionisation potential ( minimum amount of energy to remove an electron from the outermost shell ) is less. read more
Alkali metal have a strong tendency to lose electrons and act as good reducing agents. The reducing character increases from sodium to caesium. However lithium is the strongest reducing agent. Reason The alkali metals have low value of ionization energy which decreases down the group and so can easily lose their valence electron and thus act as good reducing agents. read more
In terms of pure elements, fluorine is the strongest oxidizing agent and cesium is the strongest reducing agent. (Francium may indeed by a stronger reducing agent, but there has never been enough of it in existance to prove/deny that). PtF6-, I believe, is a VERY strong oxidizing agent and is what was used to oxidize Xenon for the first time. read more