Introduction:
The reaction of oils with hydrogen in the presence of palladium or nickel catalyst is an example of an addition reaction.

Explanation:
- Addition reaction: An addition reaction is a type of chemical reaction where two or more reactants combine to form a single product. In an addition reaction, atoms or groups of atoms are added to a molecule, resulting in an increase in the number of atoms or groups of atoms in the product. The reaction between oils and hydrogen in the presence of a catalyst is an example of an addition reaction because hydrogen atoms are added to the oil molecule.

Reaction:
- In the presence of a palladium or nickel catalyst, the double bonds present in the oil molecule are broken and hydrogen atoms are added to the carbon atoms, resulting in the formation of a saturated fat molecule.
- The catalysts, palladium or nickel, facilitate the reaction by providing a surface for the reactants to come into contact and promoting the breaking of the double bonds and the addition of hydrogen atoms.

Formation of fats:
- Oils are unsaturated fats, which means they contain one or more double bonds between carbon atoms in their hydrocarbon chain. These double bonds give oils a liquid state at room temperature.
- When oils are treated with hydrogen in the presence of a palladium or nickel catalyst, the double bonds are converted into single bonds, resulting in the formation of saturated fats.
- Saturated fats have no double bonds in their hydrocarbon chain and have a solid state at room temperature.

Conclusion:
The reaction between oils and hydrogen in the presence of palladium or nickel catalyst is an example of an addition reaction. The double bonds in the oil molecule are broken, and hydrogen atoms are added to form saturated fats. This reaction is important in the food industry for the production of solid fats from liquid oils.