All inorganic reactions belong to the following two types. (i) *Redox Reactions:* Oxidation-Reduction reactions are popularly called redox reactions. **Oxidation and Reduction**(old definition): *Oxidation* is the process in which oxygen or any other nonmetal is added to a substance OR hydrogen or any other metal is removed from a substance. *Reduction* is the process in which hydrogen or any other metal is added to a substance OR oxygen or any other nonmetal is removed from a substance.Oxidation and reduction processes occur simultaneously in a reaction, which is therefore called redox reaction. *(Modern definition of oxidation-reduction on the basis of electron loss and gain will be discussed in the text for class-10. A large number of redox reactions cannot be explained by the old definitions. Hence we shall not discuss much regarding this.)*