Hi -

Although I have answered the question, I'm not sure its 100% correct so would be very grateful for expert advice please ?

Many Thanks

Several absorption transitions between energy levels of Na are indicated in the figure below. Some of these are allowed and some are not. Find the four allowed absorption transitions and, by dragging and dropping a tick or a cross into the box next to the line representing each transition, indicate them in the figure. You need to put either a tick or a cross on all boxes. X K 6d 6f 6p 6s 5d 5f 5p 4d 4f 5s 4p 3d 4s 3p energy 3s Complete the following paragraph: The diagram above shows that in Na, states with the same n but different / quantum numbers have different energies. The effect responsible for this break-up in degeneracy in Na is referred to as . Closed shells partially shield the outer electron from the nucleus. Electrons with angular momentum penetrate the closed-shell more and therefore 'see' a higher effective nuclear charge, feeling a stronger attractive force. Therefore, for a given n, the smaller / is, the lower the energy of the state