Problem 1: Positronium consists of an electron and a po

Problem 1:
Positronium consists of an electron and a positron (same mass as electron but opposite charge) orbiting around their common center of mass. The broad features of the spectrum are therefore expected to resemble those of hydrogen the differences arising largely from the mass relations. At which energy will the first three lines of the Balmer series of positronium appear?
Problem 3:
Calculate the form of the Zeeman Effect which occurs when a homogeneous magnetic field of 4.0 T (40 kG) is applied to a hydrogen atom in which the transition from the 2p- to the 3d-state is monitored. Which transitions are allowed (considering also the magnetic quantum number selection rule???? ? ml ??0?1) how many lines can be seen in the absorption spectrum and what are their energies?
Please provide me with an explanation of what are the selection rules about.
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