Saturated hydrocarbons do not show addition reaction as they are less reactive and also addition reaction is conversion of unsaturated to saturated hydrocarbon.

Unsaturated hydrocarbons show addition reactions but not saturated hydrocarbons

Introduction
Hydrocarbons are organic compounds consisting of carbon and hydrogen atoms. They are classified into two main categories based on the type of carbon-carbon bonds present in their structure: saturated hydrocarbons and unsaturated hydrocarbons. Saturated hydrocarbons have only single bonds between carbon atoms, while unsaturated hydrocarbons have at least one double or triple bond between carbon atoms.

Definition of addition reaction
An addition reaction is a type of chemical reaction in which two or more molecules combine to form a larger molecule. This reaction involves the breaking of the double or triple bond in unsaturated hydrocarbons and the addition of new atoms or groups to the carbon atoms.

Reasons why unsaturated hydrocarbons show addition reactions
1. Presence of multiple bonds: Unsaturated hydrocarbons have double or triple bonds between carbon atoms, which are relatively reactive compared to single bonds in saturated hydrocarbons. These multiple bonds provide sites for the addition of atoms or groups.

2. Electron-rich double or triple bond: The presence of double or triple bonds in unsaturated hydrocarbons results in a higher electron density around the carbon atoms involved in the multiple bond. This electron-rich nature makes these carbon atoms susceptible to attack by electrophiles, which leads to the addition of atoms or groups.

3. Formation of more stable products: Addition reactions of unsaturated hydrocarbons often result in the formation of more stable products. For example, addition of hydrogen to an unsaturated hydrocarbon forms a saturated hydrocarbon, which is thermodynamically more stable. This stability drives the addition reaction to occur.

4. Breaking of the double or triple bond: Addition reactions involve the breaking of the double or triple bond present in unsaturated hydrocarbons. This bond-breaking process is energetically favorable and provides the necessary activation energy for the reaction to occur.

Why saturated hydrocarbons do not show addition reactions
Saturated hydrocarbons do not have double or triple bonds, which are essential for the occurrence of addition reactions. The carbon-carbon single bonds in saturated hydrocarbons are relatively stable and require a significant amount of energy to break. Therefore, saturated hydrocarbons do not undergo addition reactions unless they are first converted into unsaturated hydrocarbons.

Conclusion
Unsaturated hydrocarbons show addition reactions due to the presence of double or triple bonds, their electron-rich nature, the formation of more stable products, and the breaking of the multiple bond. On the other hand, saturated hydrocarbons lack these reactive features and do not undergo addition reactions unless they are chemically modified to introduce unsaturation.