Oxidation and reduction the redox processes

Oxidation and reduction are key processes in the chemical evolution and thereby the climate system (Chapter 2.2.2.3). Oxidation is always coupled with reduction (therefore, redox as shorthand for the reduction-oxidation reaction)  

The reaction (4.145) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. Oxidation state is defined as the charge an atom might be imagined to have when electrons are counted according to the following agreed set of rules (Table 4.6)  

the oxidation state of a free element (uncombined element) is zero  

for a simple (monatomic) ion, the oxidation state is equal to the net charge on the ion  

hydrogen has an oxidation state of -i-l and oxygen has an oxidation state of -2 when they are present in most compounds and 

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