Q.Boron is unable to form BF6^3– ion. Explain.

As the smallest and first member of Group 13, boron departs sharply from the rest of its own group — a pattern the NCERT syllabus repeats across several p-block groups. Boron has no d orbitals available for bonding, which fixes its maximum covalence at exactly 4; it can never form a species like $BF_6^{3-}$, whereas aluminium and the heavier members, having accessible d orbitals, can expand their covalence beyond 4 (e.g. forming $[Al(H_2O)_6]^{3+}$). This same absence of d orbitals means boron cannot expand its coordination number to 6, so unlike every other Group 13 element, boron trihalides do NOT hydrolyse to give the octahedral $[M(H_2O)_6]^{3+}$ or even the tetrahedral $[M(OH)_4]^-$ species that Al, Ga, In and Tl readily form. Boron is also purely non-metallic — an extremely hard, high-melting black solid with several allotropic forms — whereas Al, Ga, In and Tl are all soft, low-me …