# Whlch element has the noble gas notation [Kr]5s^2 4d^2?

Krypton has atom number $36$. If 4 electrons are added, and the atom is neutral, $Z$ (the atomic number) $=$ $40$ necessarily.
If $Z$ $=$ $40$, we have zirconium metal. How did I know this? Firstly, I assumed a neutral species. $36$ + $4$ $=$ $40$. If $Z$ $=$ $40$, we know where to find it in the Periodic Table; I urge you to become familiar with it.
What if $Z$ $=$ $41$, or $Z$ $=$ $101$? What elements have I fingered?