Which element of group 13 shows anomalous behaviour?

Answer:

Boron shows anomalous behaviour in group 13 because of its small size and absence of d orbital.

Anomalous properties of boron

Boron is observed to have properties that are in contrast to the other elements of the boron family due to the following reasons:

• It has a very small size
• It has a very high ionisation enthalpy
• It has high electronegativity owing to its small size
• The absence of d-orbital in the valence shell

Some of these odd characteristics are discussed below.

• Except for boron, the compounds of the elements of the boron family-like tetrahedral [M(OH)₄]^– and octahedral [M(H₂O)₆]³⁺ (where M denotes the member of the boron family) exists in an aqueous medium.
• The maximum covalence of boron is 4 due to the absence of d orbitals.
• Boron is a metalloid, while the others are post-transition metals.
• The oxides and hydroxides of boron are acidic, while the oxides and hydroxides of the other elements in the family are amphoteric.