Question

The formula of potassium superoxide is:
A. $K{{O}_{2}}$
B. ${{K}_{2}}O$
C. ${{K}_{2}}{{O}_{2}}$
D. None of these

Answer 1

Hint: Think about what the superoxide ion contains and the general formula for oxide, peroxide, and superoxide ions when bonded with metals that have a +1 oxidation state.

Complete answer:
Usually, when an oxygen atom bonds with any metal, it naturally adopts a -2 oxidation state as this is the state in which any ion it may form is most stable. But when the formation of peroxides or superoxides takes place, this rule takes a backseat and the oxygen accepts the electrons that are given up by the alkali metals.
The general formulae when oxygen bonds with alkali metals are:
- Oxide: ${{M}_{2}}O$
Where each alkali metal atom donates one electron making the oxidation state of the oxygen atom -2.
- Peroxide: ${{M}_{2}}{{O}_{2}}$
Where each alkali metal atom donates one electron making the effective oxidation state of each oxygen atom -1.
- Superoxide: $M{{O}_{2}}$
Where the alkali metal atom donate one electron to two oxygen atoms, the effective oxidation state may be written as $-{}^{1}/{}_{2}$ but since oxidation states are usually not written in fractions, this means that one electron is shared between two oxygen atoms.
Since potassium is an alkali metal belonging to the group 1A, it will have the fixed oxidation state of +1.
So, the correct answer is “Option A”.

Additional Information:
Potassium superoxide is a yellowish-white paramagnetic substance and is one of the few examples where a stable salt is formed that contains the superoxide ion. It is used as a $C{{O}_{2}}$scrubber in respirators since it liberates oxygen and removes carbon dioxide. It decomposes if contact with moist air occurs.

Note: Please do not get confused while memorizing the fixed oxidation state of certain elements, only alkali metals, alkaline earth metals and fluorine have fixed oxidation states.
Also, while calculating the oxidation state for an oxygen atom in a superoxide ion, the oxygen atom will either have a -1 oxidation state or a 0 oxidation state due to the fact that only one electron is present to be shared between two atoms. The oxidation state $-{}^{1}/{}_{2}$ is an average representative of the fluctuating oxidation states of the two atoms involved.