Oxidation is defined as:
loss of electron
gain of electron
loss of proton
gain of proton
loss of electron
Oxidation
Oxidation and reduction reactions are used to describe the transfer of electrons in a redox reaction. When an electron is transferred from one species to another, one element loses an electron and the other gains an electron. These are called as half reaction of which one is oxidation and other is reduction.
Oxidation can be defined in terms of change in number of electrons, change in oxidation state or change in number of oxygen or hydrogen atoms. A species undergoes oxidation when oxygen is added to it or hydrogen is removed from it. Oxidation can also be defined as the loss of electrons. When electrons are lost from a species, its oxidation state increases.
The change in oxidation state is calculated to determine whether a compound undergoes oxidation or reduction.
Oxidation is defined as the loss of electrons and the gain of electrons is called reduction. Therefore, option (A) is correct and option (B) is incorrect.
Oxidation and reduction reactions are not defined based on the change in number of protons because removal of addition of protons does not cause any change in oxidation state of the compound. Therefore, option (C) and (D) are incorrect.
The correct option is (A) loss of electron.