Question

The inert gas atom in which the total number of d-electrons is equal to the difference in number of total p- and s- electrons, is:
A. He
B. Ne
C. Ar
D. Kr

Answer 1

It is a colorless, odourless noble gas present in p-block of periodic table which occurs in the composition of atmosphere in a trace amount. Its melting point is 115.78 K and boiling point is 119.93 K.

Complete step by step answer:
-Helium is an inert gas which belongs to group 18 and period 1 with atomic number 2. The electronic configuration of helium is $1{s^2}$. As the atomic number is 2 only two electrons are present in s – orbital and no other orbitals are present.
-Neon is an inert gas which belongs to group 18 and period 2 with atomic number 10. The electronic configuration of neon is $1{s^2}2{s^2}2{p^6}$. As the atomic number is 10 so total 4 electrons are present in s – orbital and six electrons are present in p – orbital. No d – orbital is present.
-Argon is an inert gas which belongs to group 18 and period 3 with atomic number 18. The electronic configuration of argon is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}$. As the atomic number is 18 so total 6 electrons are present in s – orbital and twelve electrons are present in p – orbital. No d – orbital is present.
-Krypton is an inert gas which belongs to group 18 and period 4 with atomic number 36. The electronic configuration of krypton is $1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6}$. As the atomic number is 36 so total 8 electrons are present in s – orbital and 18 electrons are present in p – orbital and 10 electrons are present in d – orbital.
-Therefore, the difference in number of electrons in s- orbital and p- orbital is equal to number of electrons in d- orbital.
$Difference = 18 - 8 = 10$
-Thus, krypton is the inert gas atom in which the total number of d-electrons is equal to the difference in number of total p- and s- electrons.
Therefore, the correct option is D.

Note:
Noble gases are the one which contain 8 electrons in their outermost electrons. Due to this they are highly stable and inert in nature. Among the inert gases only helium is the one element which does not contain 8 electrons.