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1. option B

2. ground state Fe :  [Ar] 4s² 3d⁶

Aufbau rule

Electrons occupy orbitals of the lowest energy level

Charging electrons in the sub-shell uses the following sequence:  

1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.  

So the correct choice of answer is B.

Ground state is the state of electrons filling skins with the lowest energy levels.

Excited state is the state of electrons which occupy a higher energy level

The atomic number of Fe = 26, so electrons=26

Ground state configuration of Fe : [Ar] 4s² 3d⁶ or

1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d⁶

d

explanation:

rutherford's experiment showed that the atom does not contain a uniform distribution of charge.