Question

An atom has an oxidation number of -3 in one molecule, but it has an oxidation number of +3 in a second molecule. What can we say about the electronegativities of the other atoms that make up the two molecules?

Answer 1

It's oxidation number is related to its charge.

Since this atom's charge is very negative in the 1st molecule, it is more electronegative. Which means the other atom is less electronegative.

In the 2nd molecule, it has a positive charge, so THIS atom is less electronegative. Or, you can say the OTHER atom is more electronegative.