Final answer:
An atom of zirconium has two unpaired electrons, which can be determined from its electron configuration, [Kr]4d²5s².
Step-by-step explanation:
The question is asking how many unpaired electrons are in an atom of zirconium (Zr). Zirconium is element number 40, which means it has 40 protons and, in its neutral state, 40 electrons. The electron configuration for zirconium can be written as [Kr]4d25s2. This configuration indicates that there are two electrons in the 4d subshell. These two electrons are unpaired, as they occupy two different 4d orbitals. Therefore, the answer to the question is B. 2.