(i) The electronic configuration of an atom is [Z](n-2)`f^(14)(n-1)d^(1)ns^(2)`. What is the minimum position of the atom in the periodic table and correspondingly what is the atomic number of Z?
(ii) Find the number of unpaired electrons in the atom of the element having atomic number 16.
(iii) Which of the following ions does not obey Bohr's atomic theory? `He^(2+),Li^(2+),B^(3+),Be^(3+)`.

Explanation

(i) electronic configuration of the given atom:
`(n-2)f^(1-14)(n-1)d^(0-1)ns^(2)`. So, it can be stated that the given atom belongs to f-block.
Hence, the element is of group-III B and its electronic configuration is identical with `""_(71)Lu` of the lanthanoids and `""_(103)Lr` of the actinoids.
The lowest position available to the atom of the element is 6th period and group-IIIB(3). thus, it belong to the lanthanoids and has atomic number 71.
(ii) The electronic configuration of an atom of the element with atomic number 16 is `1s^(2)2s^(2)2p^(6)3s^(2)3p_(x)^(2)3p_(y)^(1)3p_(z)^(1)`.
Thus, number of unpaired electrons is two.
(iii) `B^(3+)` does not obey bohr's atomic theory because it is a 2-electron system.