Question

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

Answer 1

When an element shares electrons with same or different elements to obtain stable electronic configuration is termed as covalency. The covalency of an atom comes out to be one if it shares one electron and covalency will be two if an atom shares two electrons.

Complete step by step answer:
Beryllium and aluminium belong to different periods in the periodic table. Beryllium belongs to the second period and aluminium belongs to the third period. Therefore, the covalency of beryllium and aluminium is different due to their electronic configuration and atomic number.
Beryllium and aluminium show a diagonal relationship in which two diagonally adjacent position elements have similar properties. The diagonal relationship is generally shown by the second and third group elements of the periodic table.
Beryllium and aluminium show almost similar properties because of diagonal relationship. Both the elements can act as Lewis acid, tendency to form covalent bonds and have the same electronegative charge on them. They form polymeric structures on reaction but their covalency varies due to difference in their electronic configuration and atomic number.
Covalency of beryllium is four due to absence of d-orbital whereas, the covalency of aluminium is upto 6 because it has vacant-orbital. Both the elements have the tendency to form covalent compounds.
Hence, beryllium and aluminium differ in exhibiting maximum covalency in compounds.
So, the correct answer is “Option C”.

Note:
The pairs, which show diagonal relationship, are lithium and magnesium, beryllium and aluminium, boron and silicon, carbon and phosphorus. Due to diagonal relationship, beryllium and aluminium both have the same charge/radius ratio.