There are many definitions for Oxidation and Reduction Chemical Reactions. The oxidation state of the element of compound changes during this process. Oxidation state is equal to the charge on the ion or element or compound.
Oxidation is defined as the chemical reaction in which an element (metal or compound) loses an electron and becomes a positive ion (cation).
2 H₂ + O₂ -> 2 H₂ O Hydrogen is oxidized and Oxygen is reduced.
Same is the case when Iron combines with oxygen and becomes Ferric oxide Fe₂ O₃ or rust.
In our body glucose (C₆ H₁₂ O₆) is oxidized and we get energy and power from that chain of such reactions. Hydrogen and carbon are oxidized.
C₆ H₁₂ O₆ + 6 O₂ ==> 6 H₂ O + 6 C O₂
Formation of oxides or halides is also called oxidation process. Those elements or compound which oxidize other elements or compounds are called oxidizing agents. When an element or compound gains a hydrogen atom, it is called oxidation too. The oxidation state increases.
When oxidized and reduced compounds exist as ions in a solution, a potential difference is developed. Corrosion of metals and rusting are oxidation reactions.
Reduction is defined as the chemical reaction, in which an element or compound gains an electron and becomes a negative (anion) ion. A reduction always occurs along with an oxidation. They occur in pairs.
When an ore (metal oxide) is heated and metal loses oxygen and becomes pure element, it is called reduction of the metal.
When a compound loses a hydrogen it is called reduction as oxidation state reduces.
Electropositive metals like iron, copper, aluminum, zinc, magnesium, sodium are reducing agents as they readily lose electrons.
2 NO₃⁻ + 10 e⁻ + 12 H⁺ in acid, on heating --> 6 H₂ O + N₂
Here NO₃ is reduced to N₂ and Hydrogen is oxidized.
The redox reactions are used in electrochemical cells (batteries).