Question

Oxide, peroxide superoxide – all the three can be formed by:
(A). $Li,K$
(B). $Na,K$
(C). $K,Rb$
(D). $Na,Cs$

Answer 1

Hint: $Li$ and $Na$ forms oxide and peroxide respectively whereas $K,Rb$ and ${\text{Cs}}$ form superoxide. And can form both oxides and peroxides. The positive field around potassium and rubidium ions is so weak that it cannot prevent the conversion of peroxide anion to superoxide anion.

Complete step by step answer:
Now the question arises what are oxides, super oxide and peroxides?
Oxides are those that contain a single atom of oxygen with $ - 2$ charge. In covalent compounds oxides are substances that contain oxygen in $ - 2$ states and it is not bonded to other oxygen atoms.
Peroxides consists of peroxide ions. Peroxide ion is a particle of two oxygen atoms bonded together and has $ - 2$ charge. Peroxides are known to be good oxidizers. In this, each oxygen atom is bonded to the other oxygen atom and to the-another atom it can be carbon or hydrogen or any other.
Super oxides consist of the same two oxygen atoms as in peroxides but have $ - 1$ charge. Super oxides are even more-stronger than the peroxides. In super oxides, oxygen seems to be in $ - 1$ oxidation state.
In given option:
(A). $Li$ can from only oxide and peroxide that , lithium oxide $\left( {L{i_2}O} \right)$ and lithium peroxide $\left( {L{i_2}{O_2}} \right)$ but K can form oxides, peroxides and superoxide too.
(B). $Na,K$ since K can form all three but $Na$ can form $N{a_2}O$ (oxide) and $N{a_2}{O_2}$ (peroxide)
(C). $K,Rb$
Both ${\text{K}}$ (potassium) and ${\text{Rb}}$ (Rubidium) can form all the three.
Oxide: ${K_2}O$ , $R{b_2}O$
Peroxide: ${K_2}{O_2}$ , $R{b_2}{O_2}$
Superoxide:$K{O_2}$ , $Rb{O_2}$
(D). $Na,Cs$ both cannot form all of the three

So, the correct answer is Option C .

Note: The oxides, peroxides and superoxides of alkali metals have the following stability order:
Oxide > peroxide > superoxide
It means that the normal oxides are the most stable for alkali metals followed by peroxides and then, super oxides.