The ground state electronic configuration of Fe^3+ is;

(1)[Ar]3d^34S^2

(2)[Ar]3d^64S^2

(3)[Ar]3d^5

(4)[Ar]3d^4rs^1

(5)3d^64S^2

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The atomic number of Fe is 26. So the electron configuration of Fe can be given as follows.

`Fe = 1S^2,2S^2,2P^6,3S^2,3P^6,3d^6,4S^2`

when it forms `Fe^(3+)` ion it will lose 3 electrons 2 from 4S and 1 from 3d.

`Fe^(3+) = 1S^2,2S^2,2P^6,3S^2,3P^6,3d^5`

As we know the electron configuration of inert gas Ar is;

`Ar = 1S^2,2S^2,2P^6,3S^2,3P^6`

So we can write the electron of Fe^(3+) as;

`Fe^(3+) = 1S^2,2S^2,2P^6,3S^2,3P^6,3d^5`

`Fe^(3+) = [Ar],3d^5`

*So the correct answer is (3)*

Fe : 1s2 2s2 2p6 3s2 3p6 4s2 3d6

therefore Fe 3+ : 1s2 2s2 2p6 3s2 3p6 3d5

wkt ; Ar : 1s2 2s2 2p6 3s2 3p6

**therefore answ is Fe 3+ : Ar ,3d5 option number 3**

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