The best reducing agent is lithium, with the maximum negative value of electrode potential. By convention, reduction potential, or the propensity to be diminished, are the normal electrode potentials.
In the alkaline medium, owing to the elimination of the hydrogen ions, the latter reaction is pushed in the forward direction, so sulphur dioxide is a more active reducing agent in the alkaline medium than in the acidic medium.
Active metals, such as sodium, magnesium, aluminium, and zinc, which have relatively limited ionisation energies and low electro-negativity, are strong reduction agents. Good reducing agents are also metal hydrides, such as NaH, CaH2, and LiAlH4, which formally contain the H- ion.