Oxidizing agents are substances that accept electrons in redox reactions, becoming reduced. They tend to have high oxidation states and strong electron affinity. Fluorine is the strongest oxidizing agent due to its high electronegativity. Common oxidizing agents include oxygen, chlorine, and ozone.
Reducing agents are substances that donate electrons in redox reactions, becoming oxidized. Metals in the alkali group are good reducing agents as they have low ionization energies and electronegativity. Lithium is the strongest reducing agent due to its small standard reduction potential. Some substances can act as both oxidizing and reducing agents depending on the reaction.