Discuss the anomalous behaviour of oxygen.

(N/A) Oxygen shows anomalous behaviour compared to other elements of Group $16$ due to its small size,high electronegativity,and the absence of $d$-orbitals in its valence shell.
$1$. Oxygen is a diatomic gas $(O_2)$ at room temperature,whereas other members of the group are polyatomic solids.
$2$. Oxygen exhibits an oxidation state of $-2$ in most compounds,except in $OF_2$ where it shows $+2$. Other members of the group show $+4$ and $+6$ oxidation states in addition to $-2$.
$3$. $H_2O$ is a liquid at room temperature due to intermolecular hydrogen bonding,while the hydrides of other elements do not exhibit such strong hydrogen bonding.
$4$. The covalency of oxygen is limited to a maximum of $2$ due to the absence of $d$-orbitals in its valence shell,whereas other elements in the group can expand their covalency beyond $4$.