Which stage description corresponds to heavy rust with pitting and scaling?

• A. Stage 1: Metal sound. Light rust or flash rust. (Bubbling of paint)
• B. Stage 2: Metal sound. Heavy Rust with and/or light pitting
• C. Stage 3: Metal unsound. Heavier rust and pitting. (Scaling)
• D. Stage 4: Metal unsound. Extensive rust and heavy pitting with holes in metal throughout.

Answer: (C)

The key idea is recognizing signs of advancing corrosion: heavier rust that forms pits, along with scaling where flakes of rust lift off the surface. When the metal is described as unsound and there is both heavier rust and visible pitting plus scaling, that combination exactly matches a stage where the rust is advanced enough to cause pits and surface scales but not yet to the point of through-holes. This places it after light surface rust and before the most severe damage where holes appear. So the description that states metal unsound with heavier rust, pitting, and scaling is the correct match for heavy rust with pitting and scaling.