Answer:
C. Sprinkle iron filings around the magnet, and observe the pattern in which the iron fillings arrange themselves.
Explanation:
In order to demonstrate the size of a magnetic field we can Sprinkle iron filings around the magnet, and observe the pattern in which the iron fillings arrange themselves. This will help us know the directions of the magnetic field lines and their density , like magnetic field lines are coming out from the NORTH pole of the magnet and they will enter SOUTH pole and inside the magnet the magnetic field lines are aligned from SOUTH to NORTH.
We also observe that magnetic field line is most dense at poles and move farther as they are away from the poles.