In gallium due to poor shielding of valence electrons by the interventing 3d-electrons, the nuclear charge becomes effective, thus, atomic radius decreases and hence, the ionisation enthalpy of gallium is higher than that of aluminium.

Due to small size of boron, the sum of its first three ionisation enthalpies is very high. This prevents it to form +3 ions and forces it to form only covalent compound. That's why boron does not exist as B³⁺ ion.

Aluminium form [AlF₆]^3- ion because of the presence of vacant d-orbitals due to which it can expand its coordination number from 4 to 6. In this complex Al undergoes sp³d² hybridisation. On the other hand, boron does not form [BF₆]^3- ion, because of the unavailability of d-orbitals as it cannot expand its coordination number beyond four. Hence, it can form [BF₄]^- ion (boron in )  [BF₄]^- ion is sp³ hybridised).

Due to strong inert pair effect, +1 oxidation state of Tl is more stable than +3. since, compounds in lower oxidation state are ionic but covalent in higher oxidation state, therefore TlCl₃ is less stable and covalent in nature but TlCl is more stable and is ionic in nature.

Due to absence of d-orbitals, Al does not show inert pair effect. Therefore, its most stable oxidation state is +3. Thus, AlCl₃ is much more stable AlCl. Further, in the solid or the vapour state, AlCl_{3 is} covalent in nature but in aqueous solutions, it ionises to form Al³⁺(aq) and Cl^-(aq)ions.