Answer: iron.
- A iron
- B copper
- C bismuth
- D water
Correct answer: A. iron
Explanation: Iron (also cobalt and nickel) is ferromagnetic; copper and bismuth are diamagnetic.
Magnetic field lines form closed loops: outside the bar magnet they run from the N pole to the S pole; inside, they continue from S back to N, so the lines never start or end anywhere.
Concept context
Bar magnets, Earth's magnetism, and how different materials respond to an external magnetic field - diamagnetic, paramagnetic, and ferromagnetic behaviour.