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