A deep, narrow corrosive attack which often cause rapid penetration of the substrate thickness.

• A. Pitting
• B. Galvanic corrosion
• C. Intergranular corrosion
• D. Uniform corrosion

Answer: (A)

The key idea here is a localized form of corrosion that creates deep, narrow pits rather than an even surface attack. Pitting corrosion occurs when the protective passive film on a metal (often stainless steel) breaks down at a small defect or defect site, typically in chloride-containing environments. Once initiation happens, pits grow inward quickly while the surrounding surface remains relatively undamaged, leading to rapid penetration of the thickness despite only a small surface area being attacked.

This explains why the description fits best: a deep, narrow corrosive attack with rapid inward penetration. In contrast, galvanic corrosion is driven by two different metals in contact and tends to cause more uniform or spread attack at the interface rather than a single deep pit; intergranular corrosion proceeds along grain boundaries, often giving a network-like pattern; and uniform corrosion wears away the surface evenly rather than forming isolated deep pits.