For an electron in a 2s subshell, only one value of mlm_lml​ is allowed.

Quick Scoop

  • The 2s subshell has:
    • Principal quantum number n=2n=2n=2
    • Azimuthal quantum number l=0l=0l=0 (this is what “s” means)
  • The magnetic quantum number mlm_lml​ can take integer values from −l-l−l to +l+l+l.
  • For l=0l=0l=0, that range is just:
    • ml=0m_l=0ml​=0

So, the 2s subshell has only one orbital , corresponding to a single allowed mlm_lml​ value: 0. Hence, the number of allowed mlm_lml​ values is 1.