1. Tardigrade
  2. Question
  3. Chemistry
  4. Assertion: Boron can only form [BF4]-, whereas aluminium forms [AlF6]3-⋅ Reason: The first member of a group of elements in the s- and p- blocks shows anomalous behaviour.

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Q. Assertion : Boron can only form $\left[BF_{4}\right]^{-}$, whereas aluminium forms $\left[AlF_{6}\right]^{3-}\cdot$
Reason: The first member of a group of elements in the $s-$ and $p$- blocks shows anomalous behaviour.

Classification of Elements and Periodicity in Properties

Solution:

The maximum covalency of first member of each group of $s$- and $p$-block elements is $4$, (due to non availability of $d$-orbitals) whereas the other members can expand their valence shell to accommodate more than four pairs of electrons (due to availability of $d$-orbitals).