How many unpaired electrons are in a mercury atom?
The electronic configuration of mercury atom is: [Xe] 4f14 5d10 6s2. Therefore, the number of unpaired electrons is just zero.
The atomic number of mercury is Z = 80. Then, his electronic configuration is like xenon (Z = 54) plus 26 more electrons. You can complete sublevel 4f (14 electrons) and 5 d (10 electrons). This means there are 2 electrons for level 6. The sublevel 6s is complete and there are no orbital half-occupied. The number of unpaired electrons is 0.