Question

Describe anomalous behaviour of fluorine with the other elements of group $17$ with reference to:
Polyhalide ions.

Answer 1

Anomalous behaviour of fluorine with the other elements of group $17$: Fluorine shows anomalous behaviour with the other elements of group $17$ due to : $\left(1\right)$ small size, $\left(2\right)$ high electronegativity and $\left(3\right)$ non-availability of d-orbitals in its valence shell.
Polyhalide ions: Because of the absence of d-orbitals in its valence shell fluorine does not combine with $F^{-}$ ions to give polyhalide ions (like $F_3^{-}$) while other members of group $17$ give such polyhalide ions like $C{l}_3^{-},B{r}_3^{-},I_3^{-},I_5^{-}$ etc. because they contain d-orbitals and also there electronegativity is low.