The correct option is **C. it is an oxidising agent**. ### Detailed Explanation: 1. **Understanding Hypochlorous Acid**: - Hypochlorous acid (HClO) is a weak acid formed when chlorine dissolves in water. It is commonly used in various applications, including disinfection and bleaching. 2. **Bleaching Action**: - The bleaching action of hypochlorous acid is primarily due to its ability to act as an oxidizing agent. An oxidizing agent is a substance that can accept electrons from another substance, leading to the oxidation of that substance. In the case of hypochlorous acid, it can oxidize colored compounds, breaking down the chromophores (the parts of molecules responsible for color) and thus removing the color. 3. **Why Option C is Correct**: - Hypochlorous acid can oxidize a variety of organic and inorganic substances. For example, it can oxidize dyes and pigments, which is why it is effective as a bleach. The oxidation process involves the transfer of electrons, which disrupts the molecular structure of the colored compounds, rendering them colorless. 4. **Why Other Options are Incorrect**: - **Option A: it is a strong acid**: - This option is incorrect because hypochlorous acid is classified as a weak acid. It does not completely dissociate in water, which is a characteristic of strong acids. Strong acids, like hydrochloric acid (HCl), fully ionize in solution, while HClO only partially ionizes. - **Option B: it yields chlorine readily in pure water**: - While hypochlorous acid can release chlorine gas under certain conditions, this is not the primary reason it is used as a bleach. The bleaching action is more directly related to its oxidizing properties rather than the release of chlorine. Additionally, in pure water, hypochlorous acid does not readily yield chlorine gas; it remains mostly in its acid form. - **Option D: it is a weak acid**: - Although this statement is true, it does not explain why hypochlorous acid is used as a bleach. Being a weak acid does not inherently provide any bleaching properties. The key factor in its effectiveness as a bleach is its ability to act as an oxidizing agent. ### Summary of Key Points: - Hypochlorous acid (HClO) is an effective bleach primarily because it acts as an oxidizing agent. - It oxidizes colored compounds, breaking down their structure and removing color. - It is a weak acid, which means it does not fully dissociate in water, but this does not contribute to its bleaching properties. - The release of chlorine is not the main reason for its use as a bleach; rather, it is the oxidation process that is crucial. ### Revision Summary: - Hypochlorous acid is an oxidizing agent, making it effective for bleaching. - It disrupts the structure of colored compounds through oxidation. - It is a weak acid and does not fully dissociate in water. - The release of chlorine is not the primary reason for its bleaching action.