Which of the following is weakest acid?
Correct answer: A. HCN
- A. HCN
- B. NH₄⁺
- C. H₂S
- D. H₂CO₃
Explanation
HCN is the correct answer because it has the lowest dissociation constant (Ka) among the given options, indicating it is the weakest acid. NH₄⁺ is the conjugate acid of NH₃ and, while it can act as an acid, it is not generally compared to molecular acids like HCN, H₂S, or H₂CO₃ in terms of acidity strength. H₂S and H₂CO₃ are both weak acids but have higher dissociation constants than HCN, meaning they donate protons more readily and are thus stronger acids than HCN.
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About Acids, Bases and Salts
Acid and base behaviour is explained through the Bronsted-Lowry transfer of protons and the Lewis donation or acceptance of electron pairs. The topic includes pH, pOH, ionisation and water equilibrium, plus salt formation and hydrolysis, where a salt solution may become acidic, basic or neutral.
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