CBSE Class 12-science Answered

1. The metal needs to be in contact with an electrolyte.
2. The presence of dissolved substances in the electrolyte is necessary. These substances can be dissolved gases such as oxygen, chlorine or bromine gases or dissolved ions such as H⁺(hydrogen ion) all of which serve as strong corrosive agents. Pure distilled water with no dissolved substances will not function as an electrolyte and metals subjected to it will not corrode.
3. The presence of a corrosion cell whereby two portions of the metal surfaces become electrically connected via an electrolyte, salt bridge etc. A portion of the metal surface then becomes anodic (corrodes) giving up metal ions and another portion becomes cathodic, gaining metal ions.