Which of the following acids would form normal salt only?

Analyze the question: A normal salt forms when all the replaceable hydrogen ions in an acid are replaced by a metal (or NH₄⁺). Acids with more than one replaceable hydrogen (dibasic or tribasic) can form acid salts as well as normal salts. So the acid that forms only a normal salt must be monobasic, with just one replaceable hydrogen.

Concept: Basicity of an acid is the number of replaceable H⁺ ions per molecule.

Check each option:

• A. Tetraoxosulphate(VI) acid, H₂SO₄: dibasic. It forms the normal salt Na₂SO₄ and the acid salt NaHSO₄.
• B. Trioxonitrate(V) acid, HNO₃: monobasic. It has one replaceable H, so it forms only the normal salt, e.g. NaNO₃. No acid salt is possible.
• C. Tetraoxophosphate(V) acid, H₃PO₄: tribasic. It forms Na₃PO₄ (normal), plus NaH₂PO₄ and Na₂HPO₄ (acid salts).
• D. Trioxosulphate(IV) acid, H₂SO₃: dibasic. It forms Na₂SO₃ (normal) and NaHSO₃ (acid salt).

Answer: Only HNO₃ is monobasic, so it forms a normal salt only.

Exam tip: "Normal salt only" means monobasic acid. Memorize the common monobasic ones: HCl, HNO₃, and CH₃COOH (ethanoic acid). Ethanoic acid has 4 hydrogens, but only the one in the –COOH group is replaceable. Any acid with 2 or more replaceable H can form acid salts.