Question

What is passive iron? How is passivity removed?

Answer 1

Some metals like silver, iron when reacts with oxygen and water vapor present in atmosphere, loses electrons and oxidizes to form corresponding oxides along with the liberation of hydrogen gas, but this can be prevented up to some extent by coating with some chemicals to make them passive.

Complete answer:
The chemical name of iron is ferrous, it has the atomic number of $28$ and is placed in the middle of the periodic table in d-block. It is a transition metal with $10$ electrons in its outermost shell. Iron, when placed in the atmosphere for a long time, loses electrons and forms iron oxide, Thus, iron gets oxidized in presence of oxygen and water vapor.
The brown layer of iron oxide will deposit on the upper layer of iron metal and the metal undergoes corrosion; this phenomenon can be known as rusting of iron.
The extent of corrosion can be reduced by coating the metals with some chemicals. When iron treated with nitric acid an insoluble metallic oxide will be formed and formed as a thin layer. This thin layer stops the chemical reaction of iron oxidation. This is called passive iron.
The passivity can be removed by treating the inert iron with rubbing of sand paper.

Note:
The passivity is a very important and useful process as the metals can be protected by stopping the deeper corrosion process. Not only iron but also other metals like silver can also be turned out as an inert metal by the process of passivity. We will generally apply paints on the iron metal to stop corrosion which is an application of passivity.