Electron pairing in atoms A question asks:


  This question refers to isolated gaseous atoms. In which atom are all electrons paired? Ba, Br, S or Si?


I thought it was Ba as its electron configuration is [Xe] 6s2.

However, the answer says Si, which seems incorrect to me.

Could someone please confirm the answer for me?

Thanks
The configuration for the free atoms is:


Ba - $\mathrm{[Xe]\ 6s^2}$
Br - $\mathrm{[Ar]\ 3d^{10} 4s^2 4p^5}$
S - $\mathrm{[Ne]\ 3s^2 3p^4}$
Si - $\mathrm{[Ne]\ 3s^2 3p^2}$


Thus:


Barium has no unpaired electrons.
Bromine has one unpaired electron in 4p subshell.
Sulfur has two unpaired electrons in the 3p subshell.
Silicon has two unpaired electrons in the 3p subshell.