${\mathrm{O}}_2$ molecule is paramagnetic. It is explained on the basis of:

Lewis dot diagram for

Hydrogen $\left({\mathrm{H}}_2\right)$.

Lewis dot diagram for water $\left({\mathrm{H}}_2\mathrm{O}\right)$.

Lewis dot diagram for the carbon dioxide $\left({\mathrm{CO}}_2\right)$.

Lewis dot diagram for methane $\left({\mathrm{CH}}_4\right)$.

Lewis dot diagram for lithium fluoride ($\mathrm{LiF}$).

Lewis electron dot structure of $\mathrm{HF}$.