Two electrons are placed into the two s orbital, right? We're not placing three electrons into our s orbital or four electrons, because only a maximum of two electrons can go into any given orbital because of this principle that we mentioned above. Now, let's look at our p orbitals. Remember, there are three p orbitals. And what Hungry tells us is that before we add two electrons into an orbital, first all the orbitals must be filled with at least one electron. And that's exactly why we first add one electron to the PX orbital.