Step 1: Understanding the Question:
The objective is to identify a false statement regarding the various mechanisms and factors affecting metallic corrosion.
Corrosion is an electrochemical process where a metal is oxidized to its ionic form, leading to its deterioration.
Step 2: Detailed Explanation:
Evaluating Statement (A): In a galvanic cell formed by two different metals, the metal with the lower standard reduction potential (more active/more negative potential) acts as the anode. Oxidation occurs at the anode, which means the metal undergoes corrosion. This is a correct statement.
Evaluating Statement (B): Stress corrosion occurs when a metal is subjected to mechanical stress. The stressed part of the metal becomes more chemically active and acts as the anode compared to the unstressed part (cathode). Thus, corrosion occurs at the stressed area. This is a correct statement.
Evaluating Statement (D): Concentration cells or differential aeration cells occur when different parts of a metal are exposed to different oxygen concentrations. The part exposed to less oxygen (e.g., the part submerged deep under water) becomes anodic and undergoes corrosion, while the part with higher oxygen exposure (near the surface) becomes cathodic. This is a correct statement.
Evaluating Statement (C): The rate of corrosion depends significantly on the relative areas of the anode and cathode. For a fixed anodic area, if the cathodic area is large, the cathodic reaction (reduction) can proceed very quickly, drawing a high current from the small anode. This results in intense, rapid corrosion at the anode. Conversely, if the cathode area is smaller, the overall rate of the redox process is limited by the small cathodic surface. Therefore, the rate of corrosion is less when the area of the cathode is smaller. Thus, statement (C) is incorrect.
Step 3: Final Answer:
Statement (C) is incorrect because a smaller cathodic area actually reduces the overall rate of corrosion compared to a larger cathodic area for a given anode.