# Multiplicity of orbitals in a magnetic field [closed]

Solving past questions preparing for a test, I am stuck at number 11. Is multiplicity the ml value

$m_l$ is the magnetic quantum number, and multiplicity refers to the number of allowed values that $m_l$ can be.
• I agree with your answer. But the number of allowed values for $m_l$ (for some $l$) is 2$l$+1 when no magnetic field is applied. As the typical hydrogen atom case. In presence of an external magnetic field there would be further lost of degeneracy. That is why I do not get why to state "in a magnetic field" in 11. I would not say that there is not split of energy levels in presence of an electric field (for example, crystal field theory). – user1420303 Sep 13 '16 at 16:01