Question

Aluminium becomes passive in
A. \[Conc.HN{{O}_{3}}\]
B. ${{H}_{2}}Cr{{O}_{4}}$
C. $HCl{{O}_{4}}$
D. All

Answer 1

Hint: Passivation is the process of creating a layer of defence on the metal's surface that shields the interior from further oxidation. Apart from Aluminium, beryllium also shows the same property because of the diagonal relationship.

Complete Step by Step Solution:
First thing we should know is that all the given compounds in the options are good oxidising agent and generally convert the metal into their respective oxides except a few, e.g. Aluminium, beryllium, etc.

The reaction of Aluminium with \[Conc.HN{{O}_{3}}\]is shown below:
\[Al+6HN{{O}_{3}}\to Al{{(N{{O}_{3}})}_{3}}+3N{{O}_{2}}+3{{H}_{2}}O\]
$Al{{(N{{O}_{3}})}_{3}}$acts as the passive layer for protection.
The reaction of Aluminium with $HCl{{O}_{4}}$ is shown below:
$Al+HCl{{O}_{4}}\to {{H}_{2}}+Al{{(Cl{{O}_{4}})}_{3}}$
\[Al{{(Cl{{O}_{4}})}_{3}}\]acts as the passive layer for protection.

In the same way Aluminium reacts with ${{H}_{2}}Cr{{O}_{4}}$to protect the metal by forming a passive film and preventing further oxidation. There after the whole discussion we can conclude that Aluminium becomes passive in all the three compounds and protects the metal from further oxidation.
Hence, the correct option is D. All the above

Additional information: It is interesting to note that not only Aluminium but other metals like Beryllium also react with the given oxidising agents in the same way because of the diagonal relationship. Certain pairings of diagonally adjacent elements in the second and third periods (the first 20 elements) of the periodic table are considered to have a diagonal relationship. Students may also consider other metals that exhibit comparable passivation. Yes, metals including chromium, nickel, and cobalt also react similarly to nitric acid.

Note: The thing to note here is that all the given compounds in the option are oxidising agents and form metal oxide when they react with them. But, there are certain metals that react with them in a way that they form a protective layer around the metal which prevents the further oxidation of the metal. So, you can memorise the name of those metals which act like the exception to the general rule. The examples of such metals are, Al, Be, Ni, Co, Cr, etc.