• # question_answer 51)   The exhibition of the highest coordination number depends on the availability of vacant orbitals in the central atom. Which of the following elements is not likely to act as central atom in$MF_{6}^{3-}$? (a) B                      (b) Al                                     (c)$Ga$                                              (d) In

(a) Boron has maximum covalency of four due to non-availability of d-orbitals. Boron does not form $MF_{6}^{3-}$ ion but it forms complex fluoride of type$BF_{4}^{-}$.