 So this is another one of those identify the Lewis acid, Lewis base pairs. In this case you see we have two molecules reacting to form one molecule. So in those two molecules we're going to have one that's an electron donor and one that's an electron acceptor. You remember the electron donors are going to be Lewis bases, the electron acceptor is going to be the Lewis acid. So if you remember, we'll be looking at all of these atoms, you can see that well oxygen and SO3, all the oxygens have their octet filled. If you can't remember, do your Messford theory. So that's what sulfur trioxide looks like and H2O of course. So they've got a full octet, right? They've got a full pseudo octet and all of these oxygens do too. So this sulfur has already expanded its valence, but we know sulfur can expand its valence. So it must be the thing that's accepting the electrons. Since nothing else can accept any more electrons around it, they have the maximum amount of electrons that they can accept. Remember those period three elements and below they can accept higher amounts of electrons to make them more or what we call expanded valence. So they'll have more substituents around it. So since this thing cannot accept electrons and this thing can, then this thing must be the Lewis acid and this thing must be the Lewis base. Does that make sense? So something that's happening, you want to think about a mechanism of the reaction, something like this is going on, okay? And then there's going to be a couple of other subsequent steps, but that would get you to something that looks like that, okay? So a lot of times it's not so obvious which one it is if it's not, kind of draw the Vesper structures that you know how to do. So let's just go ahead and level them. Which one was this, did we say? The acid, sorry. The Lewis acid is the electron acceptor, okay? You see it accepting the electrons? The Lewis base electron donor. Any questions on that one? You sure? Okay.