Question

How many unpaired electrons are present in fe3+?

Answer 1

Atomic number of Fe is 26
It's electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶( long configuration)
In short- 2 8 14 2
As it is Fe³⁺, three electrons are cancelled
New configuration is 2 8 13, as electrons are cancelled from the outer most shell.
As you can see, s shell is full, p shell is also full. But the d shell has only 5 electrons now. 
So there is only one unpaired electron present in the ion Fe³⁺


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