Question

Which one is incorrect?

a) Carbon is 1s^2 2s^2 3s^2
b) Sodium 1s^2 2s^2 2p^6 3s^1
c) Neon 1s^2 2s^2 2p^6
d) all are correct


I suggest you review this web page
http://www.webelements.com/webelements/elements/text/periodic-table/econ.html
and then develop a better understanding of what the elctron configurations mean. Clicking any element in that web page will take you to another page that tells you the electron configuration.