What is iron oxide commonly known as?

Iron oxide is commonly known as rust, which is the result of the chemical reaction of iron with oxygen in the presence of moisture. This process typically occurs when iron or its alloys, such as steel, are exposed to water and air over time, leading to the formation of reddish-brown iron oxide on the surface.

Rust is specifically the product of the oxidation of iron; as iron loses electrons to oxygen, it forms iron oxide compounds primarily known as rust. Understanding this concept is crucial in various fields, especially in metallurgy and materials science, where the prevention of rust is vital for maintaining the integrity and longevity of iron-based materials.

The other terms might relate to the processes or components surrounding rust but do not represent iron oxide itself. For instance, steel is an alloy primarily made of iron, corrosion refers to the broader process of deterioration in metals, and oxidation is the general chemical reaction between a substance and oxygen, not specific to iron alone. Thus, rust stands out as the direct and specific answer among the provided options.