Question

How many unpaired electrons are in a iron atom?

Answer 1

There are four unpaired electrons in the `3d` subshell of iron.

Explanation:

The ground state configuration of Fe is

`[Ar] 4s^2 3d^6`

The `4s` electrons are paired, and with six electrons in the `3d` subsell, Hund's rule tells us these will consist of one pair and four single, unpaired electrons.

(If you are not familiar with Hund's rule, it states that when electrons populate a set of orbitals having identical energy - such as the five `3d` orbitals - they do so by placing one electron in each orbital until all the orbitals are half-filled, then the electrons start to form pairs.)