Answer: Option (a) is the correct answer.
Explanation:
A reduction-half reaction is defined as the reaction in which there occurs gain of one or more number of electrons by a specie or element.
Or, in a reduction-half reaction there occurs loss of oxygen if it is present in a reaction.
But in a reduction-half reaction loss of electrons will always take place.
For example, [tex]CuO + Mg \rightarrow Cu + MgO[/tex]
Reduction-half reaction: [tex]Cu^{2+} + 2e^{-} \rightarrow Cu[/tex]
So here, oxidation state of copper is changing from +2 to 0. Also, loss of oxygen is occurring in the reaction equation.
Oxidation-half reaction: [tex]Mg \rightarrow Mg^{2+} + 2e^{-}[/tex]
Thus, we can conclude that in a reduction half-reaction elements gain electrons.
