Which pH value indicates a highly corrosive substance?

• A. pH 7 is neutral
• B. A pH of 0.5 or over 13.5 indicates a highly corrosive substance
• C. pH around 8 indicates base
• D. pH 5 indicates acidic

Answer: (B)

Corrosivity is driven by how far a substance’s pH is from neutral. The pH scale runs from 0 to 14, with 7 being neutral. As you move toward the extremes, the substance becomes more aggressive at damaging skin, eyes, metals, and other materials. A substance that is very acidic (pH near 0) or very basic (pH near 14) has a high potential to cause rapid chemical burns and corrosion. The example given—pH around 0.5 or, on the basic side, around 13.5—captures both ends of the scale where corrosive effects are strongest, making it the best indicator of a highly corrosive substance. In contrast, a neutral pH of 7 is not corrosive, a mild base around pH 8 is not considered highly corrosive, and a weak acid like pH 5 can be irritative but is not typically classified as highly corrosive.