Answer
The electron configurations are:
a. $Cl$ : $1s^22s^22p^63s^23p^5$ or $[Ne] 3s^23p^5$
b. $Si$ : $1s^22s^22p^63s^23p^2$ or $ [Ne] 3s^23p^2$
c. $Sr$ : $1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^2$ or $[Kr] 5s^2$
d. $O$ : $1s^22s^22p^4$ or $[He] 2s^2 2p^4$
Work Step by Step
a. $Cl$ has 17 electrons. It has 7 more electrons than its previous noble gas, $Ne$. The electrons are distributed in the orbitals to get the electronic configuration: $1s^22s^22p^63s^23p^5$ or $[Ne] 3s^23p^5$
b. $Si$ has 14 electrons. It has 4 more electrons than its previous noble gas, $Ne$. The electrons are distributed in the orbitals to get the electronic configuration: $1s^22s^22p^63s^23p^2$ or $ [Ne] 3s^23p^2$
c. $Sr$ has 38 electrons. It has 2 more electrons than its previous noble gas, $Kr$. The electrons are distributed in the orbitals to get the electronic configuration: $1s^22s^22p^63s^23p^64s^23d^{10}4p^65s^2$ or $[Kr] 5s^2$
d. $O$ has 8 electrons. It has 6 more electrons than its previous noble gas, $He$. The electrons are distributed in the orbitals to get the electronic configuration: $1s^22s^22p^4$ or $[He] 2s^2 2p^4$
