B) A Neodymium magnet (NdFeB, or Neo Magnet), the most widely-used type of rare-earth magnet , is a permanent magnet made from an alloy of Neodymium , iron & boron . Molecular formula is Nd 2 Fe 14 B to form tetragonal crystalline structure. Strength: 4000-4500 Gauss.  Neodymium magnets are very