this was a question for my chem class- and for some reason the answer was the last option. Why isn't it $\ce{Mn}$ which has the most unpaired electrons?
Which of the following species would you expect to be most
paramagnetic?
1. $\ce{Mn}$
2. $\ce{Mn^2+}$
3. $\ce{Fe^3+}$
4. Both $\ce{Mn^2+}$ and $\ce{Fe^3+}$ are the same
and more paramagnetic than $\ce{Mn}$
5. All have the same paramagnetism.
Para-magnetism: Para-magnetism refers to the electronic configuration of an atom having one or more unpaired electron. That means an atom can be called para-magnetic if it has one or more unpaired electron. Now if atom A and B has no unpaired electron they have same para-magnetism (in this case zero). If they both have one unpaired electron still they have same para-magnetism (Here it's one).
Now look at the electronic configuration of the above sated options::
$Mn :: [Ar]3d^54s^2$
$Mn^{2+} :: [Ar] 3d^5$
$Fe :: [Ar]3d^64s^2$
$Fe^{3+} :: [Ar] 3d^5$
So they all have five unpaired electron. That's why they have same paramagnetism.
