The condition required for corrosion to take place is the presence of

Explanation: For corrosion (e.g., rusting of iron) to occur, two things must be present:

• Water (moisture): acts as an electrolyte so ions and electrons can move.
• Oxygen: is reduced at the cathodic sites to form hydroxide; without O₂ rusting does not proceed.

Carbon(IV) oxide (CO₂) can speed corrosion by making the water slightly acidic, but it is not required.