Why does iron rust, and how can we stop it? Also, what's that smell when food goes bad?

Iron rusting is a common example of corrosion, which is the slow degradation of metals due to their reaction with substances in the environment, primarily oxygen and moisture. For iron, it's specifically called rusting, where iron reacts with oxygen in the presence of water to form hydrated iron(III) oxide ($Fe_2O_3 \cdot xH_2O$), a reddish-brown flaky substance. To prevent rusting, we can: 1) Painting/Oiling/Greasing: Creates a barrier against air and moisture. 2) Galvanization: Coating iron with a layer of zinc, which is more reactive and corrodes first. 3) Electroplating: Coating with other metals like chromium. 4) Alloying: Mixing iron with other metals (e.g., stainless steel).

The unpleasant smell when food goes bad is due to rancidity. This occurs when fats and oils present in food items get oxidized by atmospheric oxygen over time, leading to a change in their smell and taste. To prevent rancidity, we can: 1) Add antioxidants (substances that prevent oxidation). 2) Store food in airtight containers. 3) Refrigerate food. 4) Flush packets with nitrogen gas (e.g., potato chips) to displace oxygen.