The correct option is (c) 1 and 3 only.
Explanation
The "Potato Experiment" demonstrates the chemical effect of electric current. When an electric current passes through a conducting solution (electrolyte), chemical reactions take place at the electrodes. Vegetables like potatoes contain moisture and dissolved salts, allowing them to act as electrolytes.
Statement-wise Analysis:
- Statement 1 is Correct: The experiment proves that vegetables like potatoes can conduct electricity. The juices inside the potato contain dissolved ions that facilitate the flow of electric charge, completing the circuit.
- Statement 2 is Incorrect: When copper wires are used as electrodes, a chemical reaction occurs. A greenish-blue spot forms around the wire connected to the positive terminal (anode), not the negative terminal. This is due to the oxidation of copper and its reaction with the potato's contents. The negative terminal typically shows bubbling (hydrogen gas) but no significant color change.
- Statement 3 is Correct: Since the greenish-blue spot appears exclusively around the wire connected to the positive terminal, this specific chemical effect serves as a reliable method to identify the positive terminal of a battery or cell when the markings are concealed or absent.
Key Takeaway:
The passage of electric current through a conducting liquid causes chemical reactions. In a potato circuit using copper wires, a greenish-blue spot identifies the positive terminal.