Oxidation Number:

It is the charge (real or imaginary) which an atom appears to have when it is in combination. It may be a whole no. or fractional. An element may have different values of oxidation number depending. It depends on nature of compound in which it is present. There are some operational rules to determine oxidation number.


Addition of oxygen, removal of hydrogen, addition of electro-negative element, removal of electropositive element, loss of electrons, increase in oxidation number (de – electro nation).


Removal of oxygen, addition of hydrogen, removal of electronegative element, addition of electro positive element, gain of electrons, decrease inoxidation number (electro nation).

Redox Reactions:

A reaction in which oxidation & reduction occur simultaneously.

Oxidising Agents:

(oxidants, oxidizers). They oxidise others, themselves are reduced & gain electrons. Eq. O2, O3, HNO3, MnO2, H2O2, halogens, KMnO4, K2Cr2O7, KIO3, CIO3, FeCl3, NaOCl hydrogen ions.
[Atoms are present in their higher oxidation state.

Reducing Agents:

H2, molecular form is weak reducing agent but Nascent hydrogen is powerful. C, CO, H2S, SO2, SnCl2, sodium thio Sulphate, Al, Na, CaH2, NaBH4, LiAlH4. They reduce others, themselves get oxidised & lose electrons. Also called reductants or reducers.
[Atoms are present in their lower oxidation state.]

Both oxidizing & Reducing Agents:

SO2, H2O2, O3, NO2, etc.

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