Here it says choose the compound below that should have the highest melting point according to the ionic bonding model. So remember, highest melting point means highest lattice energy. When you break these all up into their ions, based on the groups that they're found in, we'll be able to figure out the charge. Let's see here. Remember group number and their charges.

Now we're going to say lattice energy for all of them. In absolute brackets, we have their charges multiplied together. On the bottom we're going to have the periods that they're found in. So here all I'm doing is I'm inputting the charges for each one O. Remember that's the first part we need for lattice energy, O. Here we're going to multiply. There are charges in absolute terms, so for all of them the number will be positive.

Now take the periods or rows that they're found on the periodic table and they're going to go on the bottom, but they're added together. So this would be 3+2. This would be 3+2, three plus 2 and 3+3. Now we're going to bring everything down. So this is 95. This is 15, this is 45. And finally this one here is 16.

The one with the largest lattice energy is aluminum nitride, and because of that it'll have the highest melting point. So just remember, the higher lattice energy, the higher your melting point, the higher your boiling point, and remember the lower your solubility. I know the question doesn't talk about boiling point and solubility, but it's important to remember these relationships.