Answer:
Option d. f sublevel
Explanation:
Inner transition elements includes:
Lanthanides
Actinides
Lanthanides includes elements having atomic number ranges from 52-71.
Actinides includes elements having atomic number ranges from 89-103.
Actinides and lanthanides have been placed separately in two rows below all the other elements.
General electronic configuration of lanthanides: [tex]4f^{1-14}5d^{0-1}6s^2[/tex]
General electronic configuration of actinides: [tex]5f^{1-14}6d^{0-1}7s^2[/tex]
As last electrons enters in f sub shell or sublevel, these elements are also called f-block elements.
