Answer:The answer is D
Explanation:
The inner transition elements are those in the two long rows at the bottom of the Periodic Table.
The lanthanide series starts after Ba in Period 6, and the actinide series starts after Ra in Period 7.
Thus, we would predict their electron configurations to be of the form
However, the energy levels of the ns, (n-1)d, and (n-2)f orbitals are so close in energy that there are many exceptions to our predictions
For example, here are some electron configurations.
La = [Xe]6s²5d (not [Xe]6s²4f)
Ce = [Xe]6s²4f5d (not [Xe]6s²4f²)
Pr = [Xe]6s²4f³ (as predicted)
Thus, their valence electrons can be in both s and f (and sometimes d) sublevels.
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