Oxidation and reduction 10 points!!!!!!

Oxidation and reduction always come together in one reaction. It depends which reactant you focus on. In general, oxidation means to gain the electron or increase the oxidation number. In contrast, reduction means to give away the electron or decrease the oxidatio number of the element. Therefore oxidation and reduction must be always come together. If one reactant gives away the electron, another reactant must gain it. For example,
Ca + 1/2O2 ---> CaO
In this reaction, you can call it oxidation reaction if you focus on the change of oxidation state of the calcium since its oxidation state has been changed from 0 to +2. Two electrons have been gained by oxygen. However, if you focus on oxygen, this reaction is a reduction reaction since the oxidation number of oxygen has been changed from 0 to -2. In this reaction, calcium is named as reductant and oxygen is called oxidant. In general, this kind of reaction is called redox reaction. The word redox composed of REDuction and OXidation.

However, in the case of organic chemistry, we seldom talk about oxidation number. So, oxidation usually means to give oxygen or to take away the hydrogen of the reactant. In contrast, reduction means to take away the oxygen atome or to give hydrogen atoms to the reactant.

In fact, in the real life, many reactions are redox reaction such as rusting of iron or respiration. However, there are also some reaction which involves no change of oxidation state. For example, neutralization is not a redox reaction since in this reaction, there is no change of oxidation state occurred. There is just exchange of hydrogen ions.

I hope the above information can help!

oxidation = lose electrons
reduction = gain electrons

最早時期是非常貼題的：與氧的結合稱為氧化，而從氧化物中移走氧稱為還原。
氧化 ： 2Mg + O2 ---> 2MgO
還原 ： 2PbO + C ---> Pb + CO2
後來，在不斷的發現中發覺很多化學反應有相類似的表現，例如 ：
Mg + Cl2 ---> MgCl2
現在將氧化定義為失去電子，在下面兩個反應中，鎂原子都是失去電子，所以，是氧化。
2Mg + O2 ---> 2MgO
Mg + Cl2 ---> MgCl2
而還原就是獲得電子了。
Pb2+ + 2e ---> Pb