What is a reaction that uses a catalyst?

Catalyst: Substances that change the rate of a chemical reaction and themselves remain chemically unchanged after the reaction are called catalysts.

Example:- In the process of manufacturing of ammonia Fe is used as Catalyst.

Note:- there is only one arrow. I was unable to put iron over the arrow ..

a  solution  is always transparent, light passes through with no scattering from solute particles which are molecule in size. the  solution  is homogeneous and does not settle out. a colloid is intermediate between asolution  and a  suspension. while asuspension  will separate out a colloid will not.