iron is always magnetic & a magnet attracts magnetic metals ->  a magnet will attract iron  a magnet will attract iron & the mixture is made of iron nails and aluminum nails ->  a magnet will attract the iron nails in the mixture  a magnet will not attract nonmagnetic metals & aluminum is always nonmagnetic ->  a magnet will not attract aluminum  a magnet will not attract aluminum & the mixture is made of iron nails and aluminum nails ->  a magnet will not attract the aluminum nails in the mixture  a magnet will attract the iron nails in the mixture & a magnet will not attract the aluminum nails in the mixture -> a magnet can separate the mixutre of iron nails and aluminum nails