What does the fountain experiment demonstrate?

The fountain experiment is commonly associated with demonstrating the high solubility of ammonia in water. In the experiment, ammonia gas is generated and then bubbled through water, which causes the water to rise in a tube, resembling a fountain. This visual effect showcases how readily ammonia dissolves in water, leading to a significant increase in the concentration of ammonia in the solution.

The experiment highlights the nature of ammonia as a gas that is highly soluble due to its ability to interact with water molecules. This property is important in various chemical processes and applications, particularly in the production of fertilizers and in some cleaning products.

In contrast, the other options relate to different chemical concepts. The production of nitrogen dioxide involves different reactions and does not illustrate solubility in the same way. The reaction of metals with water pertains to a different series of chemical reactions that typically produce hydrogen gas and metal hydroxides, focusing on reactivity rather than solubility. The formation of nitric acid involves separate chemical processes that may utilize nitrogen dioxide under specific conditions, but that does not align with what the fountain experiment visually demonstrates.