Question

unit review - matter and change
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what method would separate a mixture of iron filings and sugar most efficiently?
add the iron and sugar to water, decant the sugar water and then evaporate it.
pick the iron filings out by hand.
dissolve the sugar in water, then filter the iron out, then evaporate the water.
use a magnet to attract the iron.

Explanation:

Iron is ferromagnetic, so a magnet can selectively attract iron filings without altering either component, which is faster and simpler than methods involving dissolving/filtering or manual sorting. Manual picking is inefficient, and water-based methods add extra steps of dissolving, filtering, and evaporating that are unnecessary.

Answer:

Use a magnet to attract the iron.