Question

Which of the following elements forms only covalent bonds with others?
A.boron
B.aluminium
C.indium
D.thallium

Answer 1

The boron group is remarkable for patterns in electron configuration, as illustrated above, as well as the properties of certain of its members. Boron is distinguished from the other members of the group by its hardness, refractivity, and unwillingness to engage in metallic bonding.

Complete answer:
The chemical elements of the boron group include boron (B), aluminium (Al), gallium (Ga), indium (In), thallium (Tl), and perhaps the chemically uncharacterized nihonium (Nh). The boron group is distinguished by the presence of three valence electrons. The trials have also been used to describe these components.
From B to Al, the electronegativity drops, then rises slightly from Aluminium to Tl. The inadequate shielding of the intermediate d and f orbitals is to blame for this. The tendency that should be predicted is the polar opposite of electronegativity. From B to Al, the metallic quality increases somewhat, then falls slightly from Aluminium to Tl. This is due to the strong Ionization Enthalpy of group 13. In addition, the smaller the ion, the lower its Ionization Enthalpy. As a result, Aluminum is the most metallic metal. The usual reduction potentials can be used to better explain this.
There are three reasons for group 13 elements to form covalent compounds.
It's possible to use Fajan's rule. The higher the covalence, the smaller the cation.
They have extremely high ionisation enthalpies ($I{{E}_{1}}+I{{E}_{2}}+I{{E}_{3}}$), making ionic compound synthesis difficult.
Because they have higher electronegativities, the synthesis of compounds will not result in a greater electronegativity differential.
Because of the following factors, boron acts differently from the other elements in group 13.
It is quite tiny in size.
Its ionisation enthalpy is quite high.
Because of its tiny size, it possesses a high electronegativity.
The valence shell is devoid of d-orbital.
This makes Boron only to make covalent compounds.
Hence boron is the correct answer ( option a)
Boron exclusively forms covalent compounds, but aluminium and other group 13 elements may also create ionic compounds.

Hence boron is the correct answer ( option a)

Note:
Boron is a chemical element with the atomic number of five that is present in the earth's crust and throughout the solar system. Boron is classified as a metalloid. It may also be found in ceramics, flare cannons, and fibre glasses as a poor conductor of electricity. Boron comes in a variety of forms, the most common of which is amorphous boron, which is a black powder that is unreactive to oxygen, water, alkalis, and acids. When it interacts with metals, it creates borides. Boron may be found in over a hundred different minerals on the planet. Even in laboratory settings, however, it is exceedingly difficult to manufacture. Boromycin is a naturally occurring antibiotic that is based on boron. It's a Streptomyces derivative.