Here in this example question, it says provide the molecular formula for the following compound. We have magnesium sulfate all right. So Magnesium is MG. Magnesium is in Group 2A, so its charge is +2 or two plus. Now, sulfate 8 is a good indicator that this is a polyatomic ion. If you remember, sulfate is one of our common types of Tetra oxides, meaning that we have 4 oxygens involved.
All right. So SOLVE means we're dealing with sulfur. It is one of our common Tetra oxides, so it has four oxygens and it has a charge of 2 minus. The polyatomic ions can be a little bit of annoying, but again, go back and review the polyatomic ions if you don't remember them. Now we look at our Mg2+ and our SO42-. Look at the numbers within the charges.
Here we have a two and here we have a two. Remember when the numbers are the same, they just cancel out and then you combine the elements together so the two plus and the 2 minus cancel out. So what we'll have left is MgSO4, so magnesium sulfate is represented by MgSO4.