Which is the electron configuration of an atom in the ground state?

a) 1s22s12p2
b) 1s22s22p53s2
c) 1s22s23s1
d) ls22s22p63s1

D) 1s22s22p63s1 is the correct answer. 

As we all know, there are no more than 2 electrons in the s-orbital, no more than 6 electrons in the p-orbital. In order to move to another orbital, you have to fully fill electrons in one orbital, then move to the next one.

Hope this helps~