Question

An atom changes its oxidation number from +3 to -1. Is it oxidized, reduced, or neither?

Answer 1

It has been reduced. It has gained 4 electrons which is why the oxidation number has gone down 4 from +3 to -1.

Answer 2

remember this:

if the element becomes more positive, it's being oxidized
if the element becomes more negative, it's being reduced

because the atom goes from +3 to -1, it's becoming more negative, so it is reduced.