Answer: When an unsaturated hydrocarbon undergoes complete addition, the product is a saturated molecule because in unsaturated molecule double and triple bond is present so during addition reaction one carbon - carbon bond will get break down and form alkane.
Example: Ethene + H2 ⇒ Ethane
Here , ethene double bond can breakdown and form ethane.
The product when an unsaturated hydrocarbon undergoes complete addition would be a saturated molecule. These saturated hydrocarbons becomes Alkanes where these molecules are only single-bonded in contrary to unsaturated hydrocarbons which have multiple bonds between atoms.
