Question

Which of the oxides is coloured and contains $3{e^ - }$ bond?
A. MgO
B. $N{a_2}O$
C. $K{O_2}$
D. $M{n_3}{O_4}$

Answer 1

The colour of the oxide is due to the unpaired electrons present in the oxide ion. Due to the presence of unpaired electrons, it absorbs visible light and jumps from ground state to excited state.

Complete step by step answer:
Superoxide is the oxide formed by two oxygen atoms where three electrons take part in the bonding process. The general superoxide is $O_2^ -$.
The compound MgO is called magnesium oxide and the compound $N{a_2}O$ is called sodium oxide. Both the compounds are normal oxide formed of a single oxygen atom. Therefore, they do not contain three electrons and are coloured.
The compound $M{n_3}{O_4}$ is a mixed oxide where manganese shows +2 and +3 oxidation states. Therefore, it does not contain three electrons and is coloured.
The compound $K{O_2}$ is a superoxide. The total electron oxide ion is 17 electrons. It contains one electron pair due to which it absorbs visible and is colored.

Therefore, the correct option is C .

Additional information:
In super oxides $O_2^ -$, the oxidation number of oxygen is -1/2. The metal superoxides stability is dependent on the size of the metal and its electropositive character. The larger is the metal ion, more is the electropositive nature and more is the stability of superoxide.

Note: The metals like potassium (K), rubidium (Rb), barium (Ba), cesium(Cs) when burned in presence of oxygen forms stable superoxides. These superoxides are used as a strong oxidizing agent which reacts with water to form oxygen gas and hydroxide ion.