What is the basic difference between the electronic configurations of transition and inner-transition elements?

Answer

General electronic configuration of transition elements=[Noble gas] `(n-1) d^(1-10) ns^(1-2)` and for inner transition element=`(n-2)f^(1-14)(n-1)d^(0-1)ns^(0-2)` . Thus, in transition elements, last electrons enters d-orbital of penultimate shell while in inner transition element. it enter f-orbital of anti-penultimate shell.