### Correct Option: D. the litmus turns red and oxygen is evolved #### Detailed Explanation: **Electrolysis of Copper(II) Sulphate:** When copper(II) sulphate (CuSO₄) is subjected to electrolysis, it dissociates into copper ions (Cu²⁺) and sulphate ions (SO₄²⁻) in solution. The electrolysis occurs in an electrolytic cell, which consists of two electrodes: the anode (positive electrode) and the cathode (negative electrode). In this case, platinum electrodes are used, which are inert and do not participate in the reaction. **At the Anode:** During electrolysis, oxidation occurs at the anode. In the case of copper(II) sulphate, the following reactions can take place: 1. **Oxidation of Water:** At the anode, water can be oxidized to produce oxygen gas (O₂) and hydrogen ions (H⁺): \[ 2H₂O \rightarrow O₂ + 4H⁺ + 4e⁻ \] This reaction produces oxygen gas, which can be observed as bubbles forming at the anode. 2. **Oxidation of Copper Ions:** Alternatively, copper ions (Cu²⁺) can be oxidized to form copper metal, but this typically occurs at the cathode where reduction takes place. Therefore, at the anode, the oxidation of water is the primary reaction. **Effect on Litmus Solution:** When litmus solution is added to the anode compartment, the following occurs: - The production of hydrogen ions (H⁺) from the oxidation of water increases the acidity of the solution. - Litmus is a pH indicator that turns red in acidic conditions. Since the concentration of H⁺ ions increases due to the oxidation of water, the litmus solution will turn red. **Conclusion:** Thus, at the anode, we observe that oxygen gas is evolved, and the litmus solution turns red due to the increase in acidity. #### Why Other Options Are Incorrect: - **Option A: the litmus turns blue but no gas is evolved** - This option is incorrect because the litmus does not turn blue; it turns red due to the formation of H⁺ ions. Additionally, oxygen gas is indeed evolved at the anode. - **Option B: the litmus turns blue and oxygen is evolved** - This option is also incorrect for the same reason as Option A. The litmus does not turn blue; it turns red due to the acidic environment created by the H⁺ ions. - **Option C: the litmus turns blue and hydrogen is evolved** - This option is incorrect because hydrogen gas is not evolved at the anode; it is produced at the cathode during the reduction of H⁺ ions. Furthermore, the litmus does not turn blue; it turns red. ### Summary: - During electrolysis of copper(II) sulphate, oxidation occurs at the anode. - Water is oxidized to produce oxygen gas and hydrogen ions (H⁺). - The increase in H⁺ ions causes litmus to turn red, indicating an acidic solution. - Therefore, the correct answer is D: the litmus turns red and oxygen is evolved.