Which one is weak acid ?

Question

Accepted Answer

**Explanation:**

The question asks to identify the weak acid among the given options. A weak acid is an acid that does not fully ionize in an aqueous solution, meaning it only partially dissociates into its ions.

1.  **Option 1: Citric acid (Correct)**
    *   **Justification:** Citric acid (C₆H₈O₇) is an organic acid, specifically a tricarboxylic acid. Organic acids, especially carboxylic acids, are generally considered weak acids because they do not completely dissociate in water. The equilibrium for their dissociation lies far to the left, meaning only a small fraction of the acid molecules donate a proton (H⁺) to water. This partial ionization is characteristic of weak acids. Citric acid is commonly found in citrus fruits and is known for its mild acidic properties.

2.  **Option 2: Nitric acid (Incorrect)**
    *   **Reasoning:** Nitric acid (HNO₃) is a strong mineral acid. Strong acids are defined as acids that completely ionize or dissociate in an aqueous solution, donating all their protons (H⁺) to water molecules. Nitric acid dissociates almost entirely into H⁺ and NO₃⁻ ions in water, making it a strong acid.

3.  **Option 3: Sulphuric acid (Incorrect)**
    *   **Reasoning:** Sulphuric acid (H₂SO₄) is also a strong mineral acid. It is a diprotic acid, meaning it can donate two protons. Its first dissociation (H₂SO₄ → H⁺ + HSO₄⁻) is essentially 100% complete, classifying it as a strong acid. The second dissociation (HSO₄⁻ → H⁺ + SO₄²⁻) is weaker, but the overall classification of sulphuric acid as a primary acid is strong due to its complete first dissociation.

4.  **Option 4: Hydrochloric acid (Incorrect)**
    *   **Reasoning:** Hydrochloric acid (HCl) is another strong mineral acid. Like nitric acid and sulphuric acid, it completely dissociates into H⁺ and Cl⁻ ions when dissolved in water. This complete ionization is the defining characteristic of a strong acid.

Therefore, based on their ionization properties in water, Citric acid is the only weak acid among the given options, while Nitric acid, Sulphuric acid, and Hydrochloric acid are all strong acids.