The difference between a 2px and a 2py orbital should be explained using the concept of quantum numbers.
When the principal quantum number (n) is 2 or greater, the angular momentum quantum number (l) gets the value of 1 corresponding to a p subshell. When l = 1, the magnetic quantum number (ml) has three possible values: −1, 0, and +1, each corresponding to different p orbital. Therefore, there is a p subshell in every shell for which n ≥ 2 and each p subshell contains three p orbitals. The three p orbitals are labelled px, py and pz with the subscripted letters indicating the axis along which each orbital is oriented. These three p orbitals are identical in size, shape, and energy; they differ from one another only in orientation. p orbitals increase in size from 2p to 3p to 4p orbital and so on.