reducing agent(n = noun.substance) reducer, reductant - a substance capable of bringing about the reduction of another substance as it itself is oxidized; used in photography to lessen the density of a negative or print by oxidizing some of the loose silver;
is a kind of chemical agent
has particulars: hydrazine

   a substance that causes reduction of another substance in a chemical reaction, as by donating electrons or adding hydrogen atoms; as, lithium hydride is a powerful reducing agent. [PJC]

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