The following acids are monobasic EXCEPT

Analyze the question: "Monobasic" means the acid releases only one H⁺ (proton) per molecule. We need the one acid that is NOT monobasic.

Concept: Basicity is the number of replaceable (ionizable) hydrogen atoms per molecule of acid. Monobasic means 1, dibasic means 2, and tribasic means 3.

Check each option:

• A. Dioxonitrate(III) acid, HNO₂: one ionizable H, so it is monobasic.
• B. Ethanedioic acid (oxalic acid), HOOC-COOH or H₂C₂O₄: two carboxyl groups, so it releases 2 H⁺. It is dibasic.
• C. Hydrobromic acid, HBr: one H, so it is monobasic.
• D. Methanoic acid (formic acid), HCOOH: one carboxyl group, so it is monobasic.
• E. Oxochlorate(I) acid, HOCl: one ionizable H, so it is monobasic.

Answer: Ethanedioic acid is the only dibasic acid in the list, so it is the exception.

Tip: Count the –COOH groups in organic acids. Ethanoic acid has one (monobasic), ethanedioic acid has two (dibasic), and citric acid has three (tribasic). Also remember that the "di" in ethanedioic tells you there are two acid groups.