So here we have an example problem that's asking which of the following molecules is oxidized and which is reduced? And notice that we have molecule A over here and molecule B, and they are undergoing a chemical reaction. And so notice we have these 4 potential answer options over here. And so of course, what we need to recall from our last lesson video is that when it comes to oxidation-reduction reactions or redox reactions, really all we need to remember is 'Leo the lion goes ger'. And because if we remember 'Leo the lion goes ger', then we'll be able to remember that oxidation is when a substance loses electrons and reduction is when a substance gains electrons.
Looking at this reaction here between molecule A and molecule B, notice that molecule A is starting with an electron here in blue, and molecule B seems to not have those that electron. And so notice that after this reaction, molecule A is actually donating its electron to molecule B, and so molecule A is losing an electron by the end of the reaction whereas molecule B is gaining the electron. And so, because molecule B is gaining the electron that makes it reduced, and because molecule A is losing the electron by the end of the reaction that makes molecule A oxidized.
We need to choose the option that corresponds with that and notice option A says molecule A is oxidized whereas molecule B is reduced and that is going to be the correct answer to this example problem. So we can go ahead and mark A here as correct. And that concludes this example problem. So I'll see you all in our next video.