Explain the mechanism of the attraction of iron nails by a magnet when brought near them.

Iron nails, when placed near a magnet, get attracted towards it.

This happens due to the magnetic induction. We know iron is a metal having free electrons. The electrons have a spin that has a magnetic moment. Initially, when the iron nails are free that is are not placed near a magnet the magnetic spins of electrons are randomly oriented and hence the net magnetic moment is zero. But when the magnet is placed near the iron nails, the near end of the nail gets oppositely magnetised. This means that the nearer of iron nails near the North Pole becomes the South Pole &, the farther end becomes the South Pole and vice versa. The nails which are even farther for then the polarized nails acts as the magnet, and hence the nails align themselves in way the imaginary magnetic field lines would have been. The iron nails are more dense near the magnet and less dense away from the magnet.