[prince umair]

Lanthanum (atomic no 57 ) having electronic configuration Xe54 5d1 6s2
is placed in lanthanide series , why it is placed in lantanides?

why we study this element when we study lanthanides....

it has its valence electron in 'd' and 's' orbital then why it is studied in f block elements?

[tamim83]

If you looked at an energy level diagram for higher n orbitals (paying close attention to 6s, 5d, and 4f), you will see that the orbitals are extremely close in energy.  So there is some ambiguity when it comes to writing electron configurations for elements like Lanthanum. 

I am no expert on Lanthanide chemistry, but my guess is that Lanthanum's chemical properties are close to that of the Lanthanides and therefore it seems appropriate to study it along with the rest of the other elements in that series. 

[prince umair]

thanks tamim..

now i had found the correct answer of the question which i posted....

following is the answer

La resembles in most of the chemical and physical properties with the lanthanides.
the ionic radii is very close to the values obtained of the other lanthanides.
the physical occurrence of the lanthanum is with the lanthanide ores....

thanks for your answer tamim.