Question

iron article are shining when new but get coated with a reddish brown powder when left for sometime

Answer 1

because iron react with air and moisture and thus forms rust .This process of forming rust over the iron is called rusting of iron.rusting is an example of corrosion of metals

Answer 2

The main reason why the objects made of iron get coated with a reddish-brown powder when left open for some time is due to the attack of atmospheric gases such as hydrogen and oxygen on iron particles. In simple terms, when the iron is left open in the environment it comes in contact with humid air and then it responds with oxygen and forms rust.