Question

Which among the following is an oxidising agent ?
A. Oxygen
B. Hydrogen
C. Copper
D. Zinc

Answer 1

Hint: As we know the oxidizing agent is a substance that can oxidize other substances by accepting electrons. Among the options, the element which can accept electrons will be the oxidising agent. The non-metals generally have high electron gain enthalpy and thus they can easily accept electrons.

Complete step by step answer:
- It can also be defined as an oxidizing agent that is a chemical species that transfers electronegative atoms to a substrate.
- The oxidising agents oxidise other elements while reducing themselves in the process.
- We also know that the oxidizing agents will have higher electron gain enthalpy. Now let us know about the two terms electronegativity and electron gain enthalpy in brief.
- Electronegativity is described as the tendency of an atom to attract a pair of electrons which is shared in a covalent bond towards itself.
- Electron gain enthalpy is the quantity of energy released by an gaseous atom which is isolated when it accepts an electron. It can be said that more the electron gain enthalpy of an element more is the capability of that element to accept an electron.
- The electron gain enthalpy increases across the period and decreases down the group. So, the elements placed in the upper right corner of the periodic table (except for the noble gases as they are highly stable and they don’t want any more electrons to add) will have the higher electron gain enthalpy and that means they will be better oxidising agents.
Let us see all options step by step:
Oxygen: Oxygen belongs to period 2 and group 16 of the periodic table. It is placed in the upper right corner of the periodic table. It has a very high electron gain enthalpy and it can easily accept 2 electrons to attain noble gas configuration and become stable. Thus it’s a good oxidising agent and it will accept electrons reducing itself and oxidising the other element.
Let’s see this reaction for better understanding:
\[\underset{\text{Calcium}}{\mathop{2Ca}}\,+\underset{\text{Oxygen}}{\mathop{{{O}_{2}}}}\,\to \underset{\text{Calcium Oxide}}{\mathop{2CaO}}\,\]
Here the oxygen reacts with calcium to form calcium oxide. Now, oxygen gains two electrons to form oxide ion,\[\begin{align} & {{O}_{2}}\to 2O \\ & O+2{{e}^{-}}\to {{O}^{2-}} \\ \end{align}\]
Also, Calcium releases the same two electrons which will be accepted by oxygen.
\[Ca\to C{{a}^{2+}}+2{{e}^{-}}\]
Thus, we can see that oxygen will accept two electrons from calcium and hereby oxidising calcium and reducing itself. So, oxygen is an oxidising agent.
Hydrogen: Hydrogen has 1 electron and 1 proton. It can be stable by either accepting 1 electron or by releasing 1 electron. Let's see two examples.
\[\begin{align} & \underset{\text{Sodium}}{\mathop{2Na}}\,+\underset{\text{Hydrogen}}{\mathop{{{H}_{2}}}}\,\to 2\underset{\text{Sodium Hydride}}{\mathop{NaH}}\, \\ & \text{Here,} \\ & \text{Na}\to \text{N}{{\text{a}}^{+}}+{{e}^{-}} \\ & \text{And,} \\ & {{\text{H}}_{2}}\to 2\text{H} \\ & \text{H}+{{e}^{-}}\to {{\text{H}}^{-}} \\ \end{align}\]
In the above reaction, hydrogen accepts an electron and gets reduced and oxidised sodium. Thus it acts as an oxidising agent.
\[\begin{align}& \underset{\text{Hydrogen}}{\mathop{{{H}_{2}}}}\,+\underset{\text{Chloride}}{\mathop{C{{l}_{2}}}}\,\to 2\underset{\text{Hydrogen Chloride}}{\mathop{HCl}}\, \\ & \text{Here,} \\ & {{\text{H}}_{2}}\to2\text{H} \\ & \text{H}\to {{\text{H}}^{+}}+{{e}^{-}} \\ & \text{And,} \\ & C{{l}_{2}}\to 2Cl \\ & Cl+{{e}^{-}}\to C{{l}^{-}} \\ \end{align}\]

In the above reaction, Hydrogen releases an electron and gets oxidised and reduces chlorine.
Thus, it acts as a reducing agent.
Copper and zinc are metals and metals have very low electron gain enthalpy. They will release electrons to form metal cations. Thus they are reducing agents not oxidising agents.
\[\begin{align}& Cu\to C{{u}^{2+}}+2{{e}^{-}} \\ & Zn\to Z{{n}^{2+}}+2{{e}^{-}} \\ \end{align}\]

Hence, it is concluded that from the above options, option A, Hydrogen is the correct one since it acts only as an oxidising agent.

Note: Hydrogen also acts as an oxidising agent but we didn’t consider it as an oxidising agent in the answer because it also acts as a reducing agent. The tendency of hydrogen to get oxidised or reduced will depend on the electronegativity of the element it is reacting with. If the electronegativity of the other element is higher than hydrogen (for example chlorine), it will act as an oxidising agent while if the electronegativity of the other element is lower than hydrogen (for example sodium), then it will act as a reducing agent.