Question

Identify from the following reactions the reactants that undergo oxidation and reduction.
${\text{NiO}}\,{\text{ + }}\,{{\text{H}}_{\text{2}}}\, \to \,{\text{Ni}}\,\,{\text{ + }}\,{{\text{H}}_{\text{2}}}{\text{O}}$

Answer 1

Hint : The loss of electrons or an increase in the oxidation state of an atom, an ion, or any atoms in a molecule is referred to as oxidation. The gain of electrons or a decrease in the oxidation state of an atom, an ion, or any atoms in a molecule is referred to as reduction.

Complete Step By Step Answer:
Redox is a chemical reaction that involves changing the oxidation states of atoms. The actual or formal transfer of electrons between chemical species is defined by redox reactions, which usually involve one species (the reducing agent) undergoing oxidation (losing electrons) while another species (the oxidising agent) undergoes reduction (gains electrons)
Nickel has a $+ 2$ oxidation state in ${\text{NiO}}$, but this transitions to zero in ${\text{Ni}}$, resulting in nickel reduction. Here, Nickel oxide transforms into nickel. That is, the oxygen in nickel oxide is being removed. The process of removing oxygen from a substance is known as reduction, and nickel oxide is no exception.
Hydrogen has a zero-oxidation state in ${{\text{H}}_{\text{2}}}$ and a $+ 1$ oxidation state in ${{\text{H}}_{\text{2}}}{\text{O}}$. Hydrogen transforms to water. Oxygen is added to hydrogen. The addition of oxygen to a product is known as oxidation, and hence hydrogen is oxidised.
The oxygen oxidation state does not change; it was $- 2$ in ${\text{NiO}}$ and is still -2 in ${{\text{H}}_{\text{2}}}{\text{O}}$.
Hence, in the above reaction Nickel undergoes reduction and Hydrogen undergoes oxidation.

Note :
Redox reactions can happen slowly, like when rust forms, or they can happen quickly, like when fuel is burned. There are basic redox processes, such as carbon oxidation to produce carbon dioxide and more complicated redox processes, such as glucose oxidation in the human body. The redox potentials can be calculated by analysing bond energies and ionisation energies in water.