Question

if an element goes from an oxidation number of 0 to an oxidation number of -3, it is
an oxidizing agent
a reducing agent
a spectator ion
reduced then oxidized
oxidized then reduced

Explanation:

To determine the role of the element, we analyze the change in oxidation number. An oxidation number decrease (from 0 to -3) means the element gains electrons, which is reduction. An oxidizing agent is reduced (since it causes another substance to be oxidized by accepting electrons). A reducing agent is oxidized (loses electrons). A spectator ion doesn't change oxidation state. The element's oxidation number only decreases, so it's reduced, acting as an oxidizing agent.

Answer:

A. an oxidizing agent