Which of the following dissociations is that of an acid?

• A. H₂O → H⁺ + OH^–
• B. NaOH → Na⁺ + OH^–
• C. NH₃ + H⁺ → NH₄⁺
• D. HF → H⁺ + F^–

Answer: (D)

Verified step by step guidance

1. Understand the definition of an acid: An acid is a substance that donates protons (H+) when dissolved in water.
2. Examine each dissociation reaction to identify if a proton (H+) is being released.
3. For the reaction H2O → H+ + OH–, water dissociates into a proton and a hydroxide ion, but water is not typically considered an acid in this context.
4. For the reaction NaOH → Na+ + OH–, sodium hydroxide dissociates into sodium and hydroxide ions, which is characteristic of a base, not an acid.
5. For the reaction HF → H+ + F–, hydrofluoric acid dissociates into a proton and a fluoride ion, which fits the definition of an acid as it donates a proton.