The correct option for the pair of metals in the reactivity series that are usually extracted by the electrolysis of their ores is **B. magnesium and calcium**. ### Detailed Explanation 1. **Understanding the Reactivity Series**: - The reactivity series is a list of metals arranged in order of decreasing reactivity. The more reactive a metal is, the more readily it will react with other substances, including water and acids. - Metals at the top of the series (like potassium, sodium, and calcium) are very reactive, while those at the bottom (like gold and platinum) are much less reactive. 2. **Electrolysis as an Extraction Method**: - Electrolysis is a method used to extract metals from their ores when they are too reactive to be extracted by reduction with carbon or other methods. - This process involves passing an electric current through a molten or dissolved ionic compound, causing the metal ions to migrate to the electrodes where they are reduced to form the metal. 3. **Why Magnesium and Calcium?**: - Both magnesium and calcium are located high in the reactivity series, making them very reactive metals. They cannot be extracted from their ores using carbon reduction because they would react with carbon instead. - Therefore, the only viable method for extracting these metals is through electrolysis of their respective molten salts (e.g., magnesium chloride or calcium chloride). 4. **Examining the Other Options**: - **A. Magnesium and Zinc**: While magnesium is correctly paired with electrolysis, zinc is less reactive than magnesium and can be extracted using carbon reduction methods. Therefore, this option is incorrect. - **C. Copper and Zinc**: Both copper and zinc can be extracted using methods other than electrolysis. Copper can be extracted from its ores through smelting, and zinc can be extracted using carbon reduction. Thus, this option is also incorrect. - **D. Lead and Calcium**: Lead is less reactive than calcium and can be extracted using carbon reduction. Calcium, however, is correctly paired with electrolysis, but since lead does not require electrolysis, this option is incorrect. ### Summary of Key Points - **Reactivity Series**: Metals are arranged by their reactivity; more reactive metals require electrolysis for extraction. - **Electrolysis**: Used for extracting highly reactive metals like magnesium and calcium from their ores. - **Incorrect Options**: Other pairs either include metals that can be extracted by carbon reduction or do not both require electrolysis. ### Revision Summary - The reactivity series ranks metals by their reactivity. - Electrolysis is necessary for extracting highly reactive metals. - Magnesium and calcium are extracted via electrolysis due to their high reactivity. - Other options include metals that can be extracted by simpler methods, making them incorrect.