And this is five. When we see this symbol five, we think about molecular orbitals. So, once again, atomic orbitals will combine two form molecular orbitals, or also known as covalent bonds. Now, from quantum mechanics, we know that whatever number of atomic orbitals that combine, they will form the same amount of molecular orbitals. In other words, there's a conservation number that we have to take into consideration. So, because two atomic orbitals combined, we should form two molecular orbitals.