 Let's go ahead and do this one really quick. So write the correct formula for magnesium sulfide. Okay, magnesium generally will, or always, will go to Mg2 plus, like that, sulfur will always go to S2 minus plus 2 minus 2, that equals 0. So the formula must be Mgs. That's the formula for magnesium sulfide. Mercury 1 oxo. Okay, so this one might throw you for a little bit because you got the mercury 1, but even then it really shouldn't hamper you too much. Mercury is Hg. 1 means it has a plus 1 charge. Oxygen, on the other hand, always has a minus 2 charge. Okay, so if we added a plus 1 and minus 2, we wouldn't get 0, right? We need one more positive here. So 2 mercurys plus 1 oxygen equals mercury oxide. Mercury 1 oxide, so it's going to be Hg2O. Now let's do aluminum oxide. Aluminum is normally Al3 plus. Oxygen, again, is 2 minus. Okay, if we do that, we don't get 0. What we'll have to do is multiply this by 2, so 2 times 3 equals 6, and multiply this by 3, okay, because 3 times 2 equals 6. When we do that, we get Al2O3, which is aluminum oxide. And then finally, sodium is always N8 plus. Fluorine is always Cl minus. Plus 1 minus 1 equals 0, so we could just take that straight away over and N8, see ya. Hopefully it's making sense.