This video explains Generally metals react with concentration acids and bases - But viii group metals and some other transition metals react initially with concentration, acids but after some time they stop reacting. This state of non reactivity is called passivity. So passivity is defined as "the state of non - reactivity after an initial reaction is called passivity" It is classified into three types (ii) chemical (ii) mechanical and (iii) Electro chemical passivity.
chemical passivity - The passivity which is obtained due to the action of a chemical (like HNO3) on metal surface.

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