### Correct Option: A. Copper sulphate, copper and zinc ### Detailed Explanation: A Daniel cell, also known as a Daniell cell, is a type of electrochemical cell that generates electrical energy through a redox reaction. It consists of two half-cells: one half-cell contains a copper electrode immersed in a copper(II) sulfate solution, while the other half-cell contains a zinc electrode immersed in a zinc sulfate solution. 1. **Electrodes**: - **Positive Electrode (Cathode)**: In the Daniell cell, the positive electrode is the copper electrode. This is where reduction occurs, meaning that copper ions (Cu²⁺) in the solution gain electrons to form solid copper (Cu). The half-reaction at the cathode can be written as: \[ \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu (s)} \] - **Negative Electrode (Anode)**: The negative electrode is the zinc electrode. This is where oxidation occurs, meaning that solid zinc (Zn) loses electrons to form zinc ions (Zn²⁺). The half-reaction at the anode can be written as: \[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} + 2e^- \] 2. **Depolarizer**: - In the context of the Daniell cell, the term "depolarizer" refers to the substance that helps to maintain the potential difference between the electrodes by preventing the buildup of products that would otherwise slow down the reaction. In this case, copper sulfate (CuSO₄) serves as the depolarizer because it provides copper ions that can be reduced at the cathode, thus allowing the cell to continue functioning efficiently. ### Why Other Options Are Incorrect: - **Option B: Manganese dioxide, carbon and zinc**: - This option describes a different type of electrochemical cell, specifically a dry cell or alkaline battery, where manganese dioxide is used as a depolarizer. In a Daniell cell, manganese dioxide is not involved, and the electrodes are not carbon and zinc. - **Option C: Sulphuric acid, lead oxide and lead**: - This option refers to a lead-acid battery, which uses lead dioxide (PbO₂) and sponge lead (Pb) as electrodes, with sulfuric acid (H₂SO₄) as the electrolyte. This is a different electrochemical system and does not apply to the Daniell cell. - **Option D: Potassium hydroxide, nickel and iron**: - This option describes a nickel-iron battery, where potassium hydroxide (KOH) is used as an electrolyte. Nickel and iron are the electrodes in this type of battery. Again, this does not relate to the Daniell cell. ### Summary of Key Points: - The Daniell cell consists of a copper cathode and a zinc anode, with copper sulfate acting as the electrolyte. - The positive electrode (cathode) is where reduction occurs, while the negative electrode (anode) is where oxidation occurs. - The correct answer is A: copper sulfate, copper, and zinc, as it accurately describes the components of a Daniell cell. - Understanding the specific components and reactions in different types of electrochemical cells is crucial for distinguishing between them. ### Revision Summary: - **Daniell Cell Components**: Copper sulfate (depolarizer), copper (cathode), zinc (anode). - **Electrode Reactions**: Reduction at the cathode (Cu²⁺ + 2e⁻ → Cu) and oxidation at the anode (Zn → Zn²⁺ + 2e⁻). - **Common Mistakes**: Confusing the Daniell cell with other types of batteries (lead-acid, alkaline). - **Key Concept**: The role of the depolarizer in maintaining cell efficiency.