What happens to a substance if it is oxidized during a chemical reaction?
what is a reducing agent, and how would you identify it in a chemical reaction?

When a substance is oxidized, it loses some electrons in the reaction. It termed as the reducing agent. This is the substance that transfers electrons to another atom. The atoms that receives the electrons is then reduced and is called the oxidizing agent.

D. most models represent a real world object in a simpler way

I’d have to say no because without oxygen in the water the fish would all be dead. so if you want to fish for dead fish, pick the ponds with the lowest oxygen concentrations.