Range of oxidation number of group …

The common oxidation state of group 16 elements is +2, +4, +6.
The group 16 elements, also known as the chalcogens have 6 valence electrons, and hence they can achieve noble gas configuration either by gaining 2 electrons or by sharing two electrons i.e., by forming M2- ions, or forming two covalent bonds. The oxidation state of elements is defined as the number of electrons gained or lost to form a bond and its sign is the indication of ionic charge on the element. Oxygen is the most electronegative element after fluorine. The difference in electronegativity between metals and oxygen is generally very high. We know that ionic bond is formed when the difference in electronegativity of any two elements is very high. Thus, metals and oxygen combine to form a metal oxide with oxygen attaining O2- form, so the oxidation state of oxygen is mostly (-II).
Electronegativity of chalcogens decreases down the group in the periodic table. Other chalcogen elements like sulphur, selenium, and tellurium react with a more electronegative element of group 1, 2 and lanthanides i.e., the uppermost elements of group 1, 2 and lanthanides to form sulphides, selenides, and tellurides. These compounds are the most stable compounds formed by these elements. Compounds formed above can be denoted as S2-, Se2-, and Te2-. The electronegativity difference between the compounds (sulphides, selenides, and tellurides) shows that they are on the borderline of 50% ionic and 50% covalent characters as in the case of PCl5. Phosphorus pentachloride is sometimes covalent in the solid state but is ionic in the aqueous state.
The chalcogen group can also share their two electrons with another element to form two covalent bonds for example H2O,F2O,Cl2O,H2S and SCl2. In the given examples the chalcogen elements have the least electronegativity. As we can see in the case of SCl2 (the electronegativity of chlorine = 3.5 and sulphur =2.5) and the oxidation state of sulphur is (+II).