Give two examples to show the anomalous behaviour of fluorine.

Explanation

The anomalous behaviour of fluorine is due to its (i) small size, (ii) highest electronegativity, (iii) low F-F bond dissociation enthalpy and (iv) non-availability of d-orbitals in its valence shell.
The two examples are :
(i) Being the most electronegative element known, fluorine shows an oxidation state of -1. It cannot show an oxidation state of +1 (except in HOF) since there is no element more electronegative than F with which it can share its unpaired electron. Further due to absence of d-orbitalss, it cannot show higher positive oxidation states of +3, +5, and +7. In contrast, all other halogens show positive oxidation states of +1, +3, +5 and +7. besides oxidation state of -1.
Since it does not show psoitive oxidation states, therefore, fluorine does not show disproportionation reactions in the alkaline medium while other halogens do.
(b) Due to small size and high electronegativily. F forms the strongest H-bonds. As a result, HF is a liquid with a boiling point of 293 K while all other hydrogen halides are gases at room temperature.