Correct Answer - Option 1 : -1
Concept:
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The oxidation number/ oxidation state of an element in a compound is the number of charges (positive or negative) assigned to an atom in a molecule or ion according to a set of some arbitrary rules.
Rules for assigning Oxidation number:
- The oxidation number of all elements in the free state is zero.
- The most electronegative element, Fluorine has a -1 oxidation number in all compounds.
- The oxidation number of monoatomic ions is the same as its charge. For example:
- Oxidation state of Li+ , Ca2+ and Al3+ are +1, +2 and +3 respectively.
- The oxidation state of Cl- and SO42- are -1 and -2 respectively.
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Hydrogen has a +1 oxidation state in all compounds except ionic hydrides (-1 oxidation state).
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The oxidation state of oxygen is -2 in a compound except in peroxides which are -1.
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Alkali metals (Li, Na, K, etc.) always have +1, and alkaline earth metals (Be, Mg, etc.) have +2 oxidation states respectively.
- In transition metal complexes, the charge of ligands is taken into consideration.
- The ligands can be categorized into anionic, cationic, and neutral. The neutral ligands do not carry any charge.
- Some examples of ligands are:
| Ligands |
Category |
| Cl-, Br-, I-, NO3-, N3-, S2- etc |
Anionic ligands |
|
Ethylenediamine(en), water, ammonia, CO, PPh3, etc |
Neutral ligands |
| NO+, NO2+
|
Positive ligands
|
Explanation:
- H2O2 is Hydrogen peroxide.
- Peroxides are compounds having One oxygen bonded to other oxygen with linkage O-O.
- In the compound Hydrogen peroxide, there are two Hydrogen atom which says that there are two negative charges balanced by two positive charges of Hydrogen ions.
- Hence the overall charge carried by two oxygen atom is -2.
- In that respect, as the molecule is neutral as whole, we can say that each oxygen carries charge
= -2 / 2 = -1.
Hence, the oxidation number of oxygen in H2O2 is -1.
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Oxygen usually shows a -2 oxidation state in most of its compounds. But exceptions are seen in the compounds such as peroxides and superoxides.
- Superoxides are the compounds in which lowest oxidation state of oxygen which is -1/2 is seen.
- Examples of superoxides are K2O, Na2O.
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Oxygen has positive oxidation state in only one compound Oxygen difluoride - OF2. Here, the oxidation state of oxygen is +2.
