Question

Iron article are shining when new but get coated with a re
ddish brown colour when left for some time

Answer 1

This is because rust comes on the surface of the iron article after its exposed to water and oxygen (present in air) for some time.

Answer 2

iron get reacted with moisture and air present in atmosphere to form iron oxide *(rust) .And iron oxide is red in colour.. it is also called corrosion of iron