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If we use a process of elimination, we know that some choices are ridiculous.
So, Let's name a few facts:
1. Distillation is where we separate mixtures, based on how they vaporize. We boil the mixture, until one of the ingredients in the mixture vaporizes, and the other one is left behind.
Are we gonna vaporize either aluminum or iron, just to get them to separate? Lol. No way.
2. Evaporation is where the surface of a liquid changes into a gas.
I don't know about you, but I've never seen iron, or aluminum, evaporate. That'd be scary.
3. We could "observe the different densities." Yeah. We could stare at them all day long. Is that going to get them to separate? Probably not.
Given all that, we're only left with one correct choice.
And in case you still don't understand, I'll give you a hint:
The three main magnetic metals are...Iron, Nickel, and Cobalt.
When the two are mixed together, observing different densities would do exactly the same as observing your favourite tv show.
If you melt them together and bring them to the boil so they partly evaporate, collect some of the gas which bubbles up, then let the liquid and the gas cool down to solid, you'll have a pair of different alloys, both would be mixtures of iron and aluminium, but one would have more iron in it, and one would have more aluminium in it.
This is because even though one metal starts boiling first, the other is already evaporating, just not as quickly.
Since they have different boiling points, distillation could work, but it'd take loads of energy to heat the metals up enough, and really expensive equipment for distillation of substances with such high boiling points.
Your best choice is a magnet, let me explain:
Magnets attract various metals and alloys, including iron and cobalt, but not including aluminium, so if you put a magnet above a mixture of iron and aluminium filings, it'll pick the iron filings up and stick to them, but it won't do that to the aluminium, so when you take the magnet away it'll drag the iron with it but not the aluminium. she copyed from yahoo