We began by talking about Stainless Steel. Stainless Steel is normal steel, plus Chromium (which is an element) and a few other substances. When Chromium is exposed to Water, it reacts with the Oxygen in Water and forms a very thin layer of Chromium Oxide. This layer protects the rest of the steel from rusting.
Yes, yes, we know that the module doesn't directly explain how Chromium Oxide is formed! But, you will learn about these things in later classes. We hope you remember the concept of valency, because that is crucial to understand how substances such as Chromium Oxide are formed!
Check out the next module in this series! Fundamental Unit of Life 1