Question

In the group 3 to group 12 transition metals, the outermosts electron shell contains one or two electrons. However,in these metals, it is the d subshells that fill up goingacross the row. In period 4 of the table, the 3d subshellfills, and in periods 5 and 6, the 4d and 5dsubshells fill, respectively. It is important to keep in mind thatthis filling is not always regular. For example, in period 4,element 23, vanadium, has an electron configuration of [Ar]3d34s2,but element 24, chromium, has an electron configuration of[Ar]3d54s.


Why is the electron Configuration backwards. I always see it with Sfirst then d p f basically. Why is this one d then s????
Why isnt it [Ar]4s3d5 instead of [Ar]3d54s??????

Answer the specific Question I have please.