Question

Which of the following statements is most applicable to hydrogen
A. It can act as a reducing agent.
B. It can act as an oxidising agent.
C. It can act both as oxidising and reducing agent.
D. It can neither act as oxidising nor as a reducing agent.

Answer 1

Hint: In this question we will study the ability of hydrogen to act as a reducing agent and as an oxidising agent. A substance that induces oxidation by receiving electrons becomes reduced when it acts as an oxidising agent. A substance that reduces something by gaining electrons is said to be an oxidising agent.

Complete Step by Step Answer:
Hydrogen can act both as oxidising and reducing agent. When it combines with metal to generate metal hydrides, which are electrovalent compounds, it functions as an oxidising agent. In its reactions with oxides, it also serves as a reducing agent.
As oxidising agent:
$2Li+{{H}_{2}}\to 2LiH$

Here, hydrogen acts as an oxidising agent because it accepts an electron donation from the reducing agent lithium, which causes Li to be oxidised and Hydrogen to be reduced.
Similarly,
$2Na+{{H}_{2}}\to 2N{{a}^{+}}{{H}^{-}}$
$Ca+{{H}_{2}}\to Ca{{H}_{2}}$
As reducing agent:
${{H}_{2}}+{{F}_{2}}\to 2HF$

Here, hydrogen acts as a reducing agent because it donates its electrons to fluorine, which allows fluorine to be reduced.
Similarly,
$PbO+{{H}_{2}}\to Pb+{{H}_{2}}O$
$CuO+{{H}_{2}}\to Cu+{{H}_{2}}O$
The correct answer is C.

Additional Information: The term "oxidised" refers to a substance that undergoes a reaction and either gains oxygen or loses hydrogen. Alternatively, we may say that an oxidised molecule is an atom or molecule that has lost one or more electrons. The term "reduced " refers to a substance that undergoes a process in which oxygen is lost or hydrogen is taken. Or, we may say that a reduced molecule is an atom or molecule that obtains one or more electrons.

Note: Oxidised compounds or reducing agents are those in which the metal's oxidation number rises as a result of the reaction. And reduced compounds or oxidising agents are substances in which the metal's oxidation number drops as a result of the reaction. In this process, hydrogen's oxidation number falls from 0 to 1, making it an oxidising agent.