Question

Peroxide ions are present in:
A. $H_2{O}_2$
B. $Ba{O}_2$
C. $O{F}_2$
D. $H_2{S}_2{O}_8$

Answer 1

Hint: In this question we have to discuss about peroxide ion $\left({O_2}^{2-}\right)$, has a single oxygen-oxygen covalent bond and an oxidation state of $-1$ on the oxygen atom.

 Complete step by step answer:
$H_2{O}_2$ (Hydrogen peroxide): In $H_2{O}_2$, as oxidation state of hydrogen is $+1$ so the oxidation state of oxygen is$-1$. So it has peroxide ion. Hydrogen peroxide is a highly unstable compound. It is pale blue, clear liquid , slightly more viscous than water in its pure state. Its uses are bleaching agents and antiseptics.
So, Option (A) is Correct.
$Ba{O}_2$ (Barium Peroxide): In $Ba{O}_2$ as the oxidation state of barium is $+2$ so the oxidation state of oxygen is $-1$. So it has peroxide ion.
It is white powder which slowly decomposes in air and forms hydroxide and oxygen.
So, Option (B) is Correct.
$O{F}_2$ (Oxygen di-fluoride): In $O{F}_2$ , as oxidation state of fluorine is $-1$ as it is more electronegative than oxygen so the oxidation state of oxygen is $+2$. So it has no peroxide ion. Oxygen difluoride is a colourless gas with a slightly irritating odour.
So, Option (C) is Incorrect.
$H_2{S}_2{O}_8$ (Peroxydisulfuric Acid): In $H_2{S}_2{O}_8$ , two oxygen attached to each other through peroxide linkage. So it has peroxide ion.
So, (D) is also correct.

Note: The peroxide ion is a powerful hydrogen ion acceptor, making the peroxides of the alkali metals and alkaline earth metals strong bases. Solutions of these peroxides are basic because of the reaction of the peroxide ion with water, which functions as a weak acid.