**1. Historical background**

The history of oxidation reduction reactions can be traced back to the early time of the human development, since the first time that the human knew the fire and used it in their daily life, especially the Copper‐Bronze age of the human development, the early time, around 4000–8000 years ago. In that era, people were benefited by the use of copper in their life; they heated cop‐ per ores and coal in an oxidation reduction reaction by which copper ores are reduced to cop‐ per metal and coal is oxidized to carbon dioxide, and besides the production of copper, the Bronze age is also known to use clay in the production of pottery. Greeks are the first to use oxi‐ dation reduction reaction as oxidizing and reducing fire conditions for pottery making; this can be summarized as firing clay in a rich or indigent atmosphere of oxygen. Clay containing iron will turn to orange‐red if fired under rich atmosphere of oxygen due to the presence of red iron oxide (higher oxidation state) or will turn to black if fired under indigent atmosphere of oxygen when black iron oxide forms (lower oxidation state). Then, the human development jumped to the Iron Age, which is around 3000–5000 years ago, when the human for the first time used iron mainly in production of knives and bayonets which were used in their daily lives and wars. A great historic jump in the oxidation reduction reactions is the use of explosives, first used by Chinese as early as 950 A.D. It was the Chinese who first developed this deadly weapon, but around the thirteenth century, the Europeans would have jumped on the technological band wagon, using it to devastate the natives of the New World during the Age of Exploration.

A modern exploration of the oxidation reduction reaction starts formally with Georg Ernst Stahl [1] in 1697 when he proposed the phlogiston theory [2], which was based on the premise that the metals often produce a calx when heated (calx is defined by Stahl as the crumbly residue left after a mineral or metal is roasted), and phlogiston is given off whenever metals or something were burned; moreover, the calxes form metals when heated with charcoal and wood, and char‐ coal is particularly rich in phlogiston because they leave very little ash when they are burned;

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however, the theory of phlogiston was not widely accepted in the scientific media. Seventy‐five years later, Antoine‐Laurent Lavoisier (1743–1794) came with solid explanation of combustion [3]. In 1772, Lavoisier discovered that when phosphorus or sulfur is burned in air, the products are acidic in nature, and the products also weigh more than the original phosphorus or sulfur, and he came to the conclusion that the elements combine with something in the air to produce acids [4], but he could not recognize what was in the air that combined with phosphorus or sul‐ fur. In 1974, he met Joseph Priestley (the father of oxygen discovery, 1733–1804) during his visit to Paris; he told Lavoisier about the gas produced when he decomposed the compound which we now call mercury oxide. This gas supported combustion much more powerfully than normal air. Priestley believed the gas was a particularly pure version of air; he started calling it dephlo‐ gisticated air, believing its unusual properties were caused by the absence of phlogiston. In 1779, Lavoisier coined the name oxygen for the element released by decomposition of mercury oxide, and from here, explanation of certain reactions as oxidation reduction officially started [5].

Coming back to the explosive materials, the year 1964 was the year that explosives, nitrocel‐ lulose and nitroglycerin, were both discovered, and later on trinitrotoluene (TNT), involved in weapon production and widely used in the First World War (1914–1919). The cheap mixture of ammonium nitrate and fuel oil was recognized as a powerful explosive in 1955, and this was used to bomb the Federal Building in Oklahoma City in 1995; finally, the explosives that were used in the fireworks are believed to be used for the first time in China in the sixth century.

Now, the five main types of redox reactions are combinations, decompositions, displace‐ ments, combustions, and disproportionations. In combination redox reactions, two elements are combined whereas one element becomes oxidant and the other reluctant; in decomposi‐ tion redox reactions, a compound is broken down into its constituent parts; in displacement redox reactions, one or more atoms is swapped out for another; in combustion reactions, a compound reacts with oxygen to produce carbon dioxide, water, and heat; and in dispropor‐ tionation redox reactions, a molecule is both reduced and oxidized. These types of reactions are rare, and many reactions are considered in the interface between these areas.

Concluding this historical background that chemists worldwide later recognized that other ele‐ ments reacted in the same general manner as oxygen, the concepts of oxidation and reduction were extended to include other elements; electrochemistry as a new field is further broadening the definition of the oxidation reduction reaction. Investigators observed that the ferric ions could be formed from the ferrous ions by the action of oxygen gas. This consumption of oxy‐ gen, oxidation, involved a loss of electrons by the ferrous ions species, and hence, an oxidation reaction could refer also to a transfer of electrons.
