Animated Solution for Chemistry - s and p-Block Elements: The oxide that gives $H_2{O}_2$ most readily on treatment with $H_{2}O$ is

Imagine you are in a chemistry lab, tasked with producing hydrogen peroxide ($H_2{O}_2$) simply by adding a compound to water. You are given four choices: lead dioxide ($Pb{O}_2$), sodium peroxide ($N{a}_2{O}_2$), tin dioxide ($Sn{O}_2$), and barium peroxide octahydrate ($Ba{O}_2\cdot 8H_{2}O$). Which one do you choose? Let's break down the chemistry to find the perfect candidate.

Peroxides

The first step is to understand the nature of the oxygen in these compounds. To produce hydrogen peroxide, we fundamentally need a compound that already contains the peroxide ion, $O_2^{2-}$. In this ion, oxygen is in the $-1$ oxidation state.

If we look at $Pb{O}_2$ and $Sn{O}_2$, they are dioxides. The metal atoms (lead and tin) are in the $+4$ oxidation state, meaning the oxygen atoms are in the standard $-2$ oxidation state. Because they lack the peroxide linkage, they cannot yield $H_2{O}_2$ upon hydrolysis. They are simply the wrong tools for the job.

This leaves us with $N{a}_2{O}_2$ and $Ba{O}_2\cdot 8H_{2}O$. Both of these are true peroxides, containing the crucial $O_2^{2-}$ ion. However, their reactivity with water is vastly different.

Barium peroxide octahydrate ($Ba{O}_2\cdot 8H_{2}O$) is commonly used in the laboratory preparation of hydrogen peroxide, but there is a catch. If you simply add it to water, the reaction is incredibly slow. It forms a protective layer of sparingly soluble barium hydroxide ($Ba(OH{)}_2$) on its surface, which effectively halts the reaction. To make it work, you need to react it with dilute acids like $H_{2}S{O}_4$ or $H_{3}P{O}_4$ to neutralize the hydroxide and keep the reaction going.

On the other hand, sodium peroxide ($N{a}_2{O}_2$) is highly reactive. As an alkali metal peroxide, it reacts vigorously and exothermically with cold water. The moment it touches the water, it undergoes rapid hydrolysis:

This reaction is so spontaneous and releases so much heat that it is the most direct and ready way to produce hydrogen peroxide among the given options. Therefore, $N{a}_2{O}_2$ is our clear winner!