Answer:
Calcium Oxide must be Ionic, as we have one metal and one non metal involved. the metal is Calcium and the non metal is Oxygen. Meaning Calcium must be the one that transfers (loses) electrons to Oxygen, and Oxygen gains these electrons. It would look something like this:
Because Calcium transfers 2 electrons, it now has 2 more positively charged protons than the total number of electrons, as two electrons are lost. this means Calcium is no longer an atom, as it's positive protons and negative electrons can't cancel and make it neutral, it is now an ion, and a positively charged one at that. Same thing applies for Oxygen, but the opposite. because it has 2 more negative electrons than it's total of positive protons, it is now also an ion, and a negative one at that. The diagrams provided show the charges of the ions.
Potassium Nitrate must also be Ionic, for the same reason as before. the metal is Potassium and the non metal is Nitrogen. However, because Potassium is in Group 1, it only has 1 electron it can transfer to Nitrogen, but Nitrogen needs 2 electrons for a full outer energy level, therefore, we must have two Potassium atoms in this equation. It would look something like this:
Because there are two Potassium ions, each with a +1 charge, this means the overall charge of the Potassium ions is 2+, and this cancels out with the 2- provided by one ion of Nitrogen