When transition metal atoms lose electrons to form ions, the electrons come first from the highest filled s atomic orbital. with this in mind , how many unpaired electrons are present in the fe2+ ion? hint: first write the outermost electron configuration of fe atom?

The atomic number of Fe= 26

The electronic configuration of Fe will be

1s2 2s2 2p6 3s2 3p6 4s2 3d6

When it loses two electrons to form ferrous ion (Fe(II)) the electrons will be loose by 4s orbital first

So the electronic configuration of Fe^+2 ion will be

1s2 2s2 2p6 3s2 3p6  3d6

Hence there are six electrons in 3d orbital of iron dipositive ion

Now the the electrons in 3d orbital will be like:

so there are four unpaired electrons