Question

drag the missing word into place
and they have a magnetic field, north to south, you’ll find it.
it’s the area around where they exert their ,
but only on magnetic metals, of course.
force repel poles

Explanation:

The sentence is about magnets exerting a magnetic force, especially on magnetic metals. "Force" fits the context as magnets exert a magnetic force in their area (magnetic field), while "repel" is an action between poles and "poles" are parts of a magnet, not what's exerted. So the missing word is "force".

Answer:

force