Question

In which of the following compounds iron has the lowest oxidation number?
A.$FeS{O_4}.{\left( {N{H_4}} \right)_2}S{O_4}.6{H_2}O$
B.${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$
C.$F{e_2}O$
D.$F{e_2}{O_3}$

Answer 1

This question gives knowledge about oxidation number. Oxidation number is the charge present on an atom when it forms ionic bonds with different heteroatoms. Oxidation number is also termed as oxidation state.

Complete step-by-step answer: Oxidation number is the charge present on an atom when it forms ionic bonds with different heteroatoms. Oxidation number is also termed as oxidation state.
Let the oxidation state of iron be $x$.
Now, consider $FeS{O_4}.{\left( {N{H_4}} \right)_2}S{O_4}.6{H_2}O$ to determine the oxidation state of iron. Oxidation state is basically the sum of the charges of all the atoms present in the given compound. In this molecule, the oxidation state of sulphate ion is $- 2$, ammonium ion is $+ 1$ and the water molecule is $0$. The overall charge on this compound is $0$. On summing up all the charges along with their molecularity we observe that the oxidation number of iron is $+ 2$.
Consider ${K_4}\left[ {Fe{{\left( {CN} \right)}_6}} \right]$ to determine the oxidation state of iron. In this molecule, the oxidation state of cyanide ion is $- 1$ and potassium is $+ 1$ . The overall charge on this compound is $0$. On summing up all the charges along with their molecularity we observe that the oxidation number of iron is $+ 2$.
Consider $F{e_2}O$ to determine the oxidation state of iron. In this molecule, the oxidation state of oxide ions is $- 2$. The overall charge on this compound is $0$. On summing up all the charges along with their molecularity we observe that the oxidation number of iron is $+ 1$.
Consider $F{e_2}{O_3}$ to determine the oxidation state of iron. In this molecule, the oxidation state of oxide ions is $- 2$. The overall charge on this compound is $0$. On summing up all the charges along with their molecularity we observe that the oxidation number of iron is $+ 3$.
$F{e_2}O$ has the lowest oxidation number of iron.

Therefore, option $3$ is the correct option.

Note: The elements or atoms which are electronegative in nature possess negative charge and the atoms which are electropositive in nature carry positive charge. The molecularity of an atom present in a molecule also plays an important role while determining the oxidation state.