He final electron in inner transition metals enters the a. p sublevel. c. d sublevel. b. s sublevel. d. f sublevel.

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:

General electronic configuration of actinides:

As last electrons enters in f sub shell or sublevel, these elements are also called f-block elements.