Answer
After filling the subshell $3s$, the electrons must move to the next lowest-energy subshell, the $3p$, not the $3d$.
Work Step by Step
$[Ne]3s^23d^5$
The problem here is quite similar to part a). After completely filling the orbital in subshell $3s$ with 2 electrons, the electrons must move to the next lowest-energy subshell, which is the $3p$ subshell, not the $3d$ one.
Therefore, one correct electron configuration must be $[Ne]3s^23p^5$
