Reduction involves
Addition of Hydrogen
Addition of any electropositive element
Removal of oxygen
Removal of any electronegative element
Reduction is the process of addition of hydrogen or hydrogen or any electropositive element or group or removal of oxygen or any electronegative element or group. For example:
a. H2(g)+Cl2(g)[R]−→2HCl(g)
(Addition of hydrogen)
b. 2HgCl2(aq)+SnCl2(aq)[R]−→
Hg2Cl2(s)+SnCl4(aq)
(Addition of electropositive element)
c. ZnO(s)+C(s)[R]−→Zn(s)+CO(g)
(Removal of oxygen)
d. 2FeCl3(aq)+H2S(g)[R]−→
FeCl2(aq)+2HCl(aq)+S(s)
(Removal of electronegative element)
A more general definition is:
Reduction: It is a process in which an atom or a group of atoms taking part in a chemical reaction gains one or more electrons.