Which acids are graded as 4 (Severe) in the laboratory severity scale?

• A. HCl and Nitric acid
• B. Benzoic acid, Boric acid, Carbonic acid
• C. Hydrofluoric acid and Acetic acid
• D. Sulfuric acid and Phosphoric acid

Answer: (A)

The main concept is how the laboratory severity scale groups acids by their potential to cause severe harm on exposure. The highest severity category is reserved for the strongest, most corrosive acids that can cause rapid, deep tissue injury and hazardous fumes.

Concentrated hydrochloric acid and concentrated nitric acid fit this highest level because they are highly corrosive to skin and eyes and, in the case of nitric acid, also act as a strong oxidizer that can amplify tissue damage and produce toxic fumes. Their ability to cause immediate, severe injury makes them the best fit for the 4 (Severe) category.

The other acids listed tend to be weaker or have different hazard profiles. Benzoic, boric, and carbonic acids are relatively mild corrosives. Acetic acid is a weak organic acid with less aggressive tissue damage. Hydrofluoric acid is extremely dangerous due to fluoride toxicity and tissue penetration, but it is often treated as a distinct hazard because of its unique mechanism. Sulfuric and phosphoric acids are strong, but the classification on this specific scale places the most severe category with hydrochloric and nitric acids.