Question

Due to diagonal relationship between Be and Al
A) Both are metals
B) Both are metalloids
C) Both form polymeric covalent hydrides
D) None of these

Answer 1

Be belongs to alkaline earth metal group i.e. it belongs group 2 whereas aluminium belongs to the 13th group having the group valency as +3.
Consider all the similarities in the physical behavior and chemical behavior of the both elements.

Complete step by step answer:
So in the question, they have provided us with four options from which we have stated that best suit one option which is correct for the statement that, because of the diagonal relationship shown between the elements $Be$ and $Al$, they are metal, metalloids or form polymeric covalent hydrides.
Before solving the question, let’s know what a diagonal relationship means. As the name itself suggests, it is a relationship possessed mainly between the diagonally placed elements.
The element in one group is considered with another group in which the element will be one step down the group, we consider the element in the next row below the first element.
The elements which usually show the diagonal relationship are $Li$ and $Mg$ pairs and the Be and Al pairs.
So now let’s discuss the features of the diagonal relationship of $Be$ and $Al$ pair.
Be is the first element in the group -2 which possess the smallest size and have a valency of +2 but Al is the second element in the ${{13}^{th}}$ group, which possess more charge and size than the Be ion, the valency of Al is +3.But if we take the charge by size ratio of both elements, both are having almost similar value and that is the reason why they show diagonal relationship.
Due to the diagonal relationship $Be$ and $Al$ show similar characters, which is not shown by the other elements of the respective groups.
$Be$ and $Al$ forms covalently bonded polymeric hydrides, which is not a property of the alkaline earth metals since alkaline earth metals only form hydrides which are ionic in nature.
Hence we may conclude that due to the diagonal relationship Be shows a chemical property that is not shown by other group members.

So the correct answer for this question is option (C).

Note: The $Be$ and $Al$, both are metals but that is not a character which is caused due to the diagonal relationship between them. Being an alkaline earth metal, it possesses the tendency to lose two electrons to obtain the stable noble gas configuration. The metal possesses the property of losing electrons to obtain the stable configuration.
$Al$ is also a metal but it shows some properties that are shown by the metalloids hence the line between the metal character and metalloid character for the Al element is very narrow.