Discuss the anomalous behaviour of fluorine.

(N/A) Fluorine shows anomalous behaviour due to the following reasons:
$(i)$ Small atomic size.
$(ii)$ High ionization enthalpy.
$(iii)$ Absence of $d$-orbitals in the valence shell.
$(iv)$ High positive electrode potential.
Key points of anomalous behaviour:
$1$. Fluorine exhibits only a $(-1)$ oxidation state,whereas other halogens exhibit $(+1), (+3), (+5),$ and $(+7)$ oxidation states.
$2$. $HF$ is a liquid at room temperature due to intermolecular $H$-bonding,while $HCl, HBr,$ and $HI$ are gases.
$3$. Fluorine does not form polyhalide ions like $F_{3}^{-}$ due to the absence of $d$-orbitals in its valence shell.
$4$. Fluorine forms only one oxoacid $(HOF)$,whereas other halogens form several oxoacids.
$5$. The maximum covalency of fluorine is $1$ due to the absence of $d$-orbitals,while other halogens can show a covalency up to $7$.
$6$. Hydrofluoric acid $(HF)$ exists as a dimer $(H_{2}F_{2})$ and acts as a dibasic acid,while other hydrohalic acids are monobasic.
$7$. $F_{2}$ is highly reactive due to the low bond dissociation enthalpy of the $F-F$ bond.
$8$. Fluorine forms stable hexafluorides like $SF_{6}$ with sulfur,while other halogens do not form such stable hexahalides.