 OK. This next one says, bromine is the only non-metal that is a liquid at room temperature. Consider the isotope bromine 81. And it's pictured here. Select the combination which lists the correct atomic number, neutron number, and mass number respectively, OK? So the atomic number, what is that the number of? Number of protons, OK? So let's just write these things down. The number of protons is what we're looking for, OK? Then a neutron number, and then the atomic mass, OK? But AM. OK? So what is the atomic mass of bromine 81? 81 plus 35. AMU, OK? Remember, you have to have a unit, OK? So if you don't have a unit, it doesn't make sense for the mass, OK? So it's 81 AMU, OK? So now we're going to ask ourselves, well, what would be the number of protons? 35. 35, right? That's given to us when we look at the isotope here, OK? It's this here, that's the mass number. What is the mass number mean? What is that a combination of? Protons plus neutrons, right? So if we've got 81 protons plus neutrons, and we said we have 35 protons, how will we figure out the number of neutrons? Subtract, right? So we take 81 and subtract 35 from it, and we get 40. So hopefully that's one of the combinations. 35, 46, 81, and it looks like it is, OK? So any questions on that one?