Question

In the reaction $Fe + S \to FeS$
(A) Fe acts as a reducing agent
(B) S acts as an oxidising agent
(C) Fe acts as an oxidising agent
(D) Both A and B

Answer 1

Loss of electrons is known as oxidation and gain of electrons is known as reduction. The substance which itself undergoes oxidation acts as a reducing agent. Similarly, a substance which itself undergoes reduction acts as an oxidising agent.

Complete answer:
Ferrous sulphide is an ionic compound. It is formed by the transfer of electrons from iron to sulphur. It can be shown as:
$Fe - 2{e^ - } \to F{e^{2 + }} \\\ S + 2{e^ - } \to {S^{2 - }} \\\$
A force of attraction develops between the positively charged cation of iron and the negatively charged sulphide ion and ferrous sulphide is formed. As you can observe from the reactions given above, Fe loses electrons, that is, Fe is undergoing oxidation. We know that the substance which itself undergoes oxidation acts as a reducing agent. This is because, by giving away electrons, Fe is helping S to undergo reduction. So in this case, Fe is the reducing agent. Now look at sulphur. It is gaining electrons and undergoing reduction. A substance which itself undergoes reduction acts as an oxidising agent. This is because a substance can lose electrons only when there is some other chemical in the reaction mixture which is ready to accept those electrons. So here, sulphur is acting as the oxidising agent.

So the correct answer is option (D).

Note: Generally metals act as reducing agents as they tend to lose electrons and undergo oxidation. Non-metals act as oxidising agents by accepting those electrons and undergoing reduction.