From that particular list of choices, Flotation is the best. (B) Fill the trash can with water and stir it up. The nails will sink to the bottom, and the wood shavings will float on top, and you can skim them off.
But then what have you got ? You've got wet nails that'll rust if you don't dry them off in a hurry, and you've got a sticky wet pile of soggy wood shavings.
Can I suggest a better way to separate them ? Dump everything out on the ground, and pass a humongous magnet over it. The wood shavings will just lay there, but the nails will jump out and stick to the magnet. And everything will stay dry.