General electronic configuration of group `16` elements is `ns^(2) np^(4)`. To attain stable noble gas electronic configuration, all can accept two more stable noble gas electronic configuration, all can accept two more electrons, i.e. all show `-2` oxidation state. Oxygen due to high electronegativity and absence of d-orbitals in its valence shell cannot show positive oxidation states. Whereas in other elements, due to low electronegativity and presence of vacant d-orbitals, unpairing of electron occurs and shows positive oxidation states.
