Question

Identify the incorrect statement about the corrosion

• A. In the composition type of galvanic cell, metal with lower standard reduction potential undergoes corrosion
• B. In stress cell type of galvanic cell, corrosion occurs at the stressed area of the metal
• C. The rate of corrosion is more, when the area of cathode is smaller
• D. In concentration cell type of galvanic cell, the metal below the water level undergoes corrosion readily

Hint:

Remember: Small Anode + Big Cathode = Rapid Corrosion. The "sink" (cathode) is bigger than the "source" (anode).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Corrosion is an electrochemical process. The rate and location of corrosion are influenced by electrode potential, mechanical stress, and differential aeration.
Step 2: Key Formula or Approach:
Analyze each statement based on the "Small Anode, Large Cathode" rule and electrochemical principles.
Step 3: Detailed Explanation:

Statement 1: Correct. The metal with lower reduction potential (more active) acts as the anode and corrodes.
Statement 2: Correct. Stressed areas have higher energy and act as anodic regions relative to unstressed areas.
Statement 3: Incorrect. The rate of corrosion is higher when the anode area is small and the cathode area is large. A large cathode provides a vast surface for the reduction reaction, forcing the small anode to dissolve rapidly to supply enough electrons.
Statement 4: Correct. This is differential aeration. Parts of the metal with less oxygen access (underwater) become anodic and corrode, while parts with high oxygen access (above water) become cathodic.

Step 4: Final Answer:
Statement (3) is incorrect.