How many unpaired electrons are present in the atomic mercury `(Z = 80)`?

Options

A. one
B. zero
C. two
D. three

Answer

B

Explanation

Mercury has `80` electrons. It takes `(2+8+8+18 +18) = 54` electrons to complete the fifth-period elements. Strating with the sixth period, we need `2` electrons for the `6s` subshell, `14` electrons for the `4f` subshell, and `10` more for the `5d` subshell.
The total number of electrons adds up to `80`, thus, the electrons configuration of `Hg` is as follows:
`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(6)4p^(10)4f^(14)5s^(2)5p^(6) 5d^(10)6s^(2)`
or simply
`[Xe] 4f^(14) 5d^(10) 6s^(2)`
It has only paired electrons, i.e. it has zero unpaired electrons.