Question

Hydrogen gas will not reduce:
(A) heated cupric oxide
(B) heated ferric oxide
(C) heated stannic oxide
(D) heated aluminium oxide

Answer 1

In this question, by the help $OH$ electrochemical series, we will explain the reduction process. So as we know that hydrogen gas is non-toxic, colorless, odorless and non-metallic and it is a highly combustible diatomic gas with the molecule formula ${H_2}$ .

Complete step by step answer:
Electrochemical series describes the arrangement of elements in order of their increasing electrode potential values. The series that has been established by measuring the
Potential of various electrodes versus standard hydrogen electrodes (SHE).
Electrochemical series is a series of chemical elements arranged in order of their standard electrode potentials.
So from top to bottom in electrochemical series, reducing potential increases and oxidizing potential decreases.
From the series, we can see that the reducing potential of hydrogen is less than that of Aluminium.
Therefore from all this we conclude that hydrogen can't reduce Aluminium salts that are heated Aluminium Oxide in this case.
Moreover, Aluminium Oxide cannot be reduced by hydrogen even under very hot conditions because $Al$ is more active than $H$. Talking about Oxides they can be reduced by hydrogen as they are below hydrogen in the reactivity series of metal.
Aluminium is also electropositive than $H$ . $Fe$ and $\;Sn$ are also more electropositive than H but they are reduced from $F{e^{3 + }}$ to $F{e^{2 + }}$ and from $S{n^{2 + }}$ to $S{n^{2 + }}$ by just by hydrogen.

So, the correct answer is Option D.

Note: Hydrogen is a good reducing agent. When hydrogen is passed over many heated metallic oxides, they are reduced to the metals. Therefore, hydrogen reduces oxides of metal which are below in reactivity series. So that means the hydrogen can reduce the oxides of only those metals which are less reactive than hydrogen itself. Moreover, the metal oxide like Sodium Oxide, Copper Oxide which cannot be reduced by hydrogen.
Some compounds can be both reducing and oxidizing agents. Hydrogen is one of the elements that can be both reducing and oxidizing. Hydrogen gas is a reducing agent when it reacts with nonmetals and an oxidizing agent when it reacts with metals.