Which one of the following is a reducing substance?
A reducing agent is an element or compound that loses or donates electron to another chemical species in a redox reaction. If any chemical is an electron donor (reducing agent), another must be an electron recipient (oxidizing agent). A reducing agent is oxidized because it loses electrons in the redox reaction.
In the formation of iron(III) oxide
4Fe + 3O2 → 2Fe23+O32−
Iron (Fe) has an oxidation number of 0 before and 3+ after the reaction. For oxygen (O), the oxidation number began as 0 and decreased to 2−. Iron (Fe) has been oxidized because the oxidation number increased. Iron is the reducing agent because it gave electrons to the oxygen (O2). Oxygen (O2) has been reduced because the oxidation number has decreased and is the oxidizing agent because it took electrons from iron (Fe).
Potassium permanganate (KMnO4) is a strong oxidizing agent. Potassium dichromate, K2Cr2O7, is most commonly used as an oxidizing agent in various laboratory and industrial applications.
The correct option is B.