What is the electronic configuration of La⁺? Second IP of La is most likely to second IP of which element:
  
  (1) Be
  (2) Ba
  (3) Ca
  (4) Zn


The given answer is calcium. I don't understand if the 6s electron or the 5d electron leaves on ionization. Any help is appreciated.
During ionization only the electrons in last shell leaves.So its 6s