What is the electronic configuration of the element with `(i) Z= 57 .` Is it a d- or f- block element ?

Explanation

As explained in the foot the note on page `3//14` the electronic configuration of
` ( La = 57 ) " is " 1 s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(10) 4s^(2) 4p^(6) 4d^(10) 5s^(2) 5s^(6) 6s^(2) 5d^(1)`
instead of the expected `1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(10) 4s^(2) 4p^(6) 4d^(10) 5s^(2) 6s^(2) 4f^(1)`
Since the last electron enters the 5d- orbital it is called d- block element and not the f-block element .