The rust or corrosion that occurs with most metals is the result of

• A. Reaction with air
• B. Electrochemical potential difference
• C. Tendency for them to return to their natural state
• D. Moisture content

Answer: (C)

Metals tend to move toward a more stable, lower-energy state by reacting with elements in their surroundings. When iron is exposed to air and moisture, it oxidizes to iron oxides (rust) because those oxide forms are thermodynamically more stable than the pure metal. The driving force is the metal’s desire to reach that more stable state, so electrons flow to the oxidizer and a corrosion layer forms. Moisture helps by acting as an electrolyte that lets ions move, and oxygen from the air supplies the oxidizer; electrochemical potential differences can speed the process, but the core reason rust occurs is the metal’s tendency to become more stable by forming oxides.