Question

Beryllium and aluminium exhibit many properties which are similar. But, the two elements differ in:
(A) Maximum covalency in compounds
(B) Forming polymeric hydrides
(C) Forming covalent halides
(D) Exhibiting amphoteric nature in their oxides

Answer 1

There is the diagonal relationship between elements of period second and elements of period third of the periodic table. The diagonal elements of these two periods show similar characteristics in many properties.

Complete step by step answer:
The diagonal relationship between period second and period third generates a pair between two diagonally adjacent elements of both the periods. They exhibit similar properties in many aspects. This phenomenon occurs because on moving down the group the atomic size increases and on moving across a period atomic size decreases if we move diagonally from an element by one position the effect of both moving across a period and moving down a group cancels out each other hence resulting in the formation of pair of two atoms which have similar chemical properties due to negligible change in atomic size.
Now in the above question we are provided with two elements, one is beryllium which is situated in group second and period second and aluminium which is situated in group thirteen and period three both these elements form a diagonal pair and hence have similar characteristics in many aspects. But beryllium does not contain d-orbital which is present in aluminium, aluminium does consist of an empty d-orbital. The vacant d-orbital of aluminium results in accommodating a total of six electrons and making its valency 6. But in beryllium, there is no vacant d-orbital and therefore it can accommodate only four electrons having valency 4. And hence the maximum covalency in aluminium and beryllium differ from each other.
Option A is correct.

Note:
The maximum covalency of an atom is the total number of an atom it can bond through covalent bonding. An atom having a vacant orbital can accommodate an electron which results in increasing its valency compared to others.