What is Reducing agent?

Reducing agent (also called a reductant or reducer) is the element or compound in a reduction-oxidation (redox) reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized". This means that there must be an "oxidizer"; because if any chemical is an electron donor (reducer), another must be an electron recipient (oxidizer). Thus reducers are "oxidized" and oxidizers are "reduced".
The reducing agent in this reaction is ferrocyanide ([Fe(CN)6]4-). It donates an electron, becoming oxidized to ferricyanide ([Fe(CN)6]3-), simultaneously the oxidizer chlorine is reduced to chloride.
In organic chemistry, reduction more specifically refers to the addition of hydrogen to a molecule, though the aforementioned definition still applies.
Characteristics of Reducing agent
Strong reducing agents easily lose (or donate) electrons. An atom with a relatively large atomic radius tends to be a better reductant. In such species, the distance from the nucleus to the valence electrons is so long that these electrons are not strongly attracted. These elements tend to be strong reducing agents. Good reducing agents tend to consist of atoms with a low electronegativity, the ability of an atom or molecule to attract bonding electrons, and species with relatively small ionization energies serve as good reducing agents too. "The measure of a material to oxidize or lose electrons is known as its oxidation potential".The table below shows a few reduction potentials that could easily be changed to oxidation potential by simply reversing the sign. Reducing agents can be ranked by increasing strength by ranking their oxidation potentials. The reducing agent is stronger when it has a more positive oxidation potential and weaker when it has a negative oxidation potential. The following table provides the reduction potentials of the indicated reducing agent at 25 °C.
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