Final answer:
In the ground state of a Zr atom, there are 2 unpaired electrons in the 4d orbitals, following the electron configuration [Kr]4d²5s².
Step-by-step explanation:
The number of unpaired electrons in the ground state of a zirconium (Zr) atom is 2. Zirconium has an atomic number of 40, which means it has 40 electrons in its neutral ground state. The electron configuration for Zr can be written as [Kr]4d²5s². There are two electrons in the 4d orbitals that are unpaired because the 4d subshell can hold up to ten electrons and only two are present in the ground state of Zr. Therefore, the correct answer is D)2, meaning there are two unpaired electrons in the ground state of a Zr atom.