Question

Hydrogen behaves as an oxidising agent in its reaction with:
A.Chlorine
B.Potassium
C.Nitrogen
D.sulphur

Answer 1

Oxidising agents are the substances which oxidises other substances, by increasing their oxidation state and accepting electrons from them. Hydrogen can act as an oxidising agent as well as a reducing agent depending on the corresponding reagent or reactant.

Complete step by step answer:
Oxidising agents can be defined as those agents or chemical compounds which have the ability to accept the electrons of the other substances, in other words, they oxidise the other substances and it itself gets reduced. Some of the common oxidising agents are hydrogen peroxide, oxygen and the halogens.
Now if we consider the options which are given in the question we can see that the first option says chlorine. So we will look at the reaction which takes place when chlorine reacts to hydrogen.
$C{{l}_{2}}+{{H}_{2}}\to 2HCl$
Now if we look at the oxidation state of chlorine, it was $0$ when it was present in molecular form in the reactant and after reaction the oxidation state of chlorine becomes $-1$. Since, the oxidation state decreases, we can say that chlorine is getting reduced in this reaction. Hence, the option A would be incorrect, as the hydrogen is supposed to oxidise the corresponding reagent.
Now if we consider option C, the option says nitrogen. So we will look at the reaction which takes place, when nitrogen reacts to hydrogen,
${{N}_{2}}+3{{H}_{2}}\to 2N{{H}_{3}}$
Now, if we consider the oxidation states of nitrogen before and after reaction, it is $0$ in case of reactance and $-1$ in case of ammonia. So, just like chlorine, nitrogen is also getting reduced, hence this option would be an incorrect one, as hydrogen is acting as a reducing agent rather than an oxidising agent.
Now consider the second option potassium, let us consider the reaction which goes on between potassium and hydrogen,
$2K+{{H}_{2}}\to 2KH$
Here we can notice that the potassium was in zero oxidation state in the reactant and it becomes $+1$ in the product. Since, the oxidation state increases, we can say that the potassium is undergoing oxidation, hence the hydrogen is acting as an oxidising agent in this case. So this option would be the correct one
Finally if we consider the last option, the reaction between sulphur and hydrogen is,
$S+{{H}_{2}}\to {{H}_{2}}S$
We can see that the oxidation state of sulphur decreases from zero to $-2$, as it goes from reactant to product. Hence the hydrogen is acting as a reducing agent and this option is also incorrect.

So the correct option would be option C.

Note: When a reagent undergoes the process of oxidation, its oxidation number becomes positive, as it loses electrons to become the oxidised product.
-On the other hand when a reagent gains electrons it becomes reduced and consequently its oxidation number decreases.