# What is the common oxidation state of oxygen atom?

Given the elements in the p-block (such as $\text{B", "C", "N", "O", "F}$ from row 2), they are arranged in increasing atomic number from left to right, and the number of electrons increases with the number of protons (proportional to atomic number) from left to right to balance charges and improve stability.
$\text{Li}$ has one valence electron, $\text{Be}$ has two, and so on until $\text{O}$, which has six.
In order to become more stable, oxygen wants to lose or gain electrons so that it achieves an "octet," meaning a full set of 8 electrons in its highest-energy orbitals. To do so, neutral oxygen ($\text{O}$) must gain two electrons.
Each electron adds one ($-$) charge, so two electrons gives $\textcolor{b l u e}{{\text{O}}^{2 -}}$.