Selenium's most common oxidation state is -2, as it is both a non metal, and is located in the Periodic Table in the same group as O and S.
Oxidation number of Se is +6. Oxidation number of O is -2.
In compounds such as H2Se yes it is, and the oxidation number ofd -2 is well known. However there are many compounds where Se has other oxidation numbers (Se is very similar to Sulfur another group 16 elemnt) for example compounds where Se has an ox number of +4, SeF4, +6, SeF6, -1 in the polyselenide compound Na2Se2
The oxidation number of Se in K2SeO4 is +6. This is determined by considering the oxidation numbers of K(+1) and O(-2) in the compound and using the overall charge of the compound (zero) to calculate the oxidation number of Se.
The oxidation state of chloride (Cl) is -1. As a halogen, chloride is usually found with an oxidation state of -1 in most compounds.
The oxidation state of calcium is +2.
The oxidation state of carbon in methanol (CH3OH) is +2. This is because oxygen has an oxidation state of -2 and hydrogen has an oxidation state of +1, so the carbon must have an oxidation state of +2 to balance the charges in the molecule.
O = -2 oxidation state H = +1 oxidation state
2 oxidation state
The oxidation state of calcium in calcium hydride is +2, as calcium typically forms ionic compounds with a +2 oxidation state.
S = +4 oxidation state O = -2 oxidation state
Platinum is connected to two anionic Chloride ligands and two neutral Ammine ligands Platinum = +2 oxidation state Chlorine = -1 oxidation state Nitrogen = -3 oxidation state Hydrogen = +1 oxidation state
Zinc is in oxidation state +2 and oxygen in oxidation state -2. Zinc Oxide itself has not net charge/oxidation state.