Explanation

(c)
Aufbau principle states that in the ground state of an atom, the orbital with lower energy is filled up first before the filling of the orbitals with a higher energy commences.
Increasing order of energy of various orbitals is
$1s,2s,2p,3s,\ 3p,4s,3d,4p,5s,\ldots etc.$
Therefore,
[table] $\upharpoonleft$ | | ⥮ | $\upharpoonleft$ | $\upharpoonleft$ [/table]
Is not obeyed by aufbau principle. Without fully filling of $s$-subshell electrons cannot enter in $p$-subshell in ground state of atom.