Question

what is Rust how it is formed

Answer 1

Rust is like a type of corrosion.When iron comes in contact with oxygen and water it reacts together chemically to form a reddish brown flaky substance called rust.The chemical formula of rust is Fe2O3. So in order to prevent rusting nowadays they give a zinc coating to iron by the process of Galvanization.
Hope this helps!

Answer 2

Rust is a mixture of water, iron and oxygen  which can be formed by a redox reaction. it  is a product  of hydrated iron. It form when there is no paint on iron sheets. In another way, when water molecules come in the contact of oxygen molecules on iron then it form rust. Chemical equation of rust is:
2Fe + 3O2 → 2FeO3