[填空题]
Which of the following electron configuz gu94-b: :pqixeo(ge rations are not allowed:
bl 7iz2vzg+;n;sy b6 q (a) $1s^2\,2s^2\,2p^4\,3s^2\,4p^2$;
(b) $1s^2\,2s^2\,2p^3\,3s^1$;
(c) $1s^2\,2s^2\,2p^6\,3s^2\,3p^3\,4s^2\,4d^3\,4f^1$?
If not allowed, explain why.
