Rust is caused by which type of chemical reaction?

Rust is the result of an oxidation reaction, where iron reacts with oxygen in the presence of moisture to form iron oxide, commonly known as rust. This process occurs when iron is exposed to water and air and involves the transfer of electrons. During this reaction, the iron (metal) loses electrons and gains oxygen, leading to the formation of corrosion products that are typically reddish-brown in color.

Understanding this, the reason oxidation is identified as the cause of rust is due to the essential role that oxygen plays in the corrosion process. Without the presence of oxygen, the formation of rust will not occur, highlighting that oxidation is a critical and necessary aspect of rust formation. This also explains the increased susceptibility of iron to rusting in humid conditions, where moisture facilitates the oxidation process.

The other types of chemical reactions listed, such as reduction, hydrolysis, and combustion, involve different chemical processes that do not directly lead to the formation of rust. Reduction refers to gaining electrons, hydrolysis involves the breakdown of compounds by reaction with water, and combustion represents a rapid reaction with oxygen that produces heat and light, none of which specifically leads to the corrosion of iron.