Respuesta :
Answer: When an atom in a reactant gains electrons Its oxidation number decreases.
Explanation:
Oxidation number decreases when an atom gains an electrons. This type of reaction is called Reduction reaction. In this number of electrons increases in an atom.
For example:
[tex]Fe^{3+}+1e^-\rightarrow Fe^{2+}[/tex]
Here iron's oxidation state change to from+3 to +2 by gaining one electron.