Question

The stability order of oxide, peroxide, and superoxide of alkali metal is:
A. normal oxide > superoxide > peroxide
B. normal oxide > peroxide > superoxide
C. superoxide > peroxide > normal oxide
D. peroxide > normal oxide > superoxide

Answer 1

The cations with larger sizes are stabilized by anions with the larger size. The order of the increasing size of the anion is oxide < peroxide < superoxide. The stability of oxide, peroxide, and superoxide varies from moving down in the group of the periodic table.

Complete step by step answer:
The formula of oxides is ${O^{ - 2}}$. The stability of oxides decreases as we move down in the group. So the most stable metal oxide will be lithium.
The formula of peroxide is $O_2^{2 - }$. The stability of peroxide varies as we move from top to bottom in the group. First, it increases, and then it decreases on moving down in the group. Sodium peroxide is the most stable of the metal peroxides.
The formula of the superoxide is $O_2^{ - 1}$. In superoxide, the stability decreases as we move down in the group. The most stable superoxides are potassium, cesium.
Thus the stability order of oxide, peroxide, and superoxide of alkali metal is
normal oxide > peroxide > superoxide
Therefore, the correct option is B.

Note:
Lithium ions have large charge density, therefore it attracts the negative ion strongly and as a result, it is not able to accept an atom to form peroxide. Sodium ion has a weak positive field around so it forms peroxide. As the positive field around the cations of potassium is weaker, therefore, the oxide ion takes two extra electrons to form superoxide.