Atomic number of iron is 26.
a) To which group of the periodic table does iron belong? [1 Mark]
b) What is the oxidation state of iron in Fe₂O₃? [1 Mark]
c) Write down the subshell electronic configuration of the ion of iron with this oxidation state. [1 Mark]

a)
The electronic configuration of iron is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶
In its electronic configuration, iron has 4 shells, placing it in the 4th period.
Iron is a d block element so to determine the group number we need to add the electrons in the outermost s subshell and the number of electrons in the preceding d subshell. So, the group number is 6+2 = 8. [1 mark]

b) In Fe₂O₃ we know that the oxidation number of oxygen is -2.
As the total charge of the compound is '0' we can write

2Z + [3*(-2)] = 0 [ Z= oxidation number of iron]
Z= +3
So the oxidation number of iron in Fe₂O₃ is +3
[1 Mark]
c) $F{e}^{+}$${}^3$ will contain 3 electons less than Fe atom.
So, the electronic configuration will be
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵
[1 Mark]