Final answer:
To neutralize an atom with an oxidation number of -3, you need three atoms with a +1 oxidation number, as the total charge needs to be zero.
Step-by-step explanation:
If an atom has an oxidation number of -3, to create a neutral compound, it must react with atoms that contribute a total positive oxidation number equal to +3. Since we're considering atoms with a +1 oxidation number, we simply divide the total required positive charge (+3) by the oxidation number of the reacting atoms (+1).
In this case: 3 (required charge) / 1 (oxidation number of each atom) = 3. Therefore, it would require three atoms with an oxidation number of +1 to react with the atom having an oxidation number of -3 to create a neutral compound.