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In the case of organic compounds, what is meant by oxidation-reduction, is the change in the number of carbon-heteroatom bonds and carbon-hydrogen bonds. By calculating the difference in the number of carbon-heteroatom bonds of reactant and product or by calculating the difference in the number of carbon-hydrogen bonds in the reactant and product, it can be found whether the reactant has been oxidized or reduced.

If the number of carbon-heteroatom bonds increases and the number of the carbon-hydrogen bond decreases in going from reactants to products, the reactant is said to be oxidized. This is because when carbon makes a bond with a more electronegative heteroatom, its electron density is decreased, and thus oxidation occurs.

On the other hand, If the number of carbon-heteroatom bonds decreases or the number of the carbon-hydrogen bonds increases in going from reactants to products, the reactant is said to be reduced. This is because, when carbon makes a bond with hydrogen, it gains electron density, so it is said to be reduced.

In the given reaction, 2-hexene is giving 2,3-duhydroxyhexane, which is oxidation, as there are 12 C-H bonds in 2-hexene but 2 C-OH bonds in the product 2,3-dihydroxyhexane.i.e., the number of C-O bonds is increasing.

In the given reaction, cyclohexane is giving benzene, which is oxidation, as there are 12 C-H bonds in cyclohexane while 6 C-H bonds. i.e., the number of C-H bonds is decreasing.