Under what condition do amphoteric metals not corrode?

Amphoteric metals, such as aluminum and zinc, can behave as either acids or bases depending on the pH of their environment. They have the unique ability to form stable oxides or hydroxides that can act as barriers to further corrosion.

The correct condition under which amphoteric metals do not corrode is when the pH is between 6 and 8. In this pH range, amphoteric metals can maintain a protective oxide layer that prevents further oxidation or reaction with the surrounding environment. This stable oxide layer effectively mitigates corrosion because it reduces the reactivity of the metal.

When the pH falls below 6 or rises above 8, these metals can either start to dissolve in acidic conditions or lose their protective oxide layer in highly alkaline conditions, leading to increased corrosion rates. In alkaline solutions, for example, the increased concentration of hydroxide ions can disrupt this equilibrium and enhance the corrosion process instead of protecting the metal. Therefore, the pH range between 6 and 8 is critical for maintaining the stability and protective qualities of amphoteric metals, ensuring they do not corrode.