Wat is rusting of iron

When iron is exposed to water or air over a period of time, the iron reacts with oxygen in the presence of moisture to form a reddish-brown chemical compound, iron oxide. This is referred to as rust. So chemically, rust is hydrated iron(III) oxide or Fe₂O₃.nH₂O.
Iron reacts very readily with oxygen. This is one of the reasons as to why it is rare to find pure iron in nature.
Factors Affecting Rusting:
There are several factors that assist and accelerate the process of rusting. Some of them are:
(i) Moisture: Iron exposed to rains is the most common reason.
(ii) Acid: It accelerates rusting. When exposed to acid rains, iron rusts faster. On the other hand, alkalis inhibit rusting.
(iii) Salt: Iron tends to rust faster in sea, due to the presence of salt.
(iv) Impurity: Pure iron rusts slower than the iron mass which contains a mixture of metals.