$\mathrm{H}_2 \mathrm{SO}_4$ acts as a catalyst for decomposition of $\mathrm{H}_2 \mathrm{O}_2$. Therefore, some weaker acids such as $\mathrm{H}_3 \mathrm{PO}_4, \mathrm{H}_2 \mathrm{CO}_3$ is preferred over $\mathrm{H}_2 \mathrm{SO}_4$ for preparing $\mathrm{H}_2 \mathrm{O}_2$ from peroxides.

$$3 \mathrm{BaO}_2+2 \mathrm{H}_3 \mathrm{PO}_4 \longrightarrow \underset{\text { (insoluble) }}{\mathrm{Ba}_3\left(\mathrm{PO}_4\right)_2}+3 \mathrm{H}_2 \mathrm{O}_2 $$

In water, oxygen has $s p^3$-hybridisation and the bond angle of HOH should have been $109^{\circ} 28^{\prime}$. In $\mathrm{H}_2 \mathrm{O}$, the oxygen atom is surrounded by two shared pairs and two lone pairs of electrons. From VSEPR theory, lone pair - lone pair repulsions are stronger than bond pair-bond pair repulsions.

As a result, the bond angle of HOH in water slightly decreases from the regular tetrahedral angle of $109^{\circ} .28^{\prime}$ to $104.5^{\circ}$.

Fluorine is a strong oxidising agent, it oxidises $\mathrm{H}_2 \mathrm{O}$ to $\mathrm{O}_2$ or $\mathrm{O}_3$. The reactions are as follows

$$\begin{aligned} 2 \mathrm{~F}_2(g)+2 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow \mathrm{O}_2(g)+4 \mathrm{H}^{+}(a q)+4 \mathrm{~F}^{-}(a q) \\ 3 \mathrm{~F}_2(g)+3 \mathrm{H}_2 \mathrm{O}(l) \longrightarrow \mathrm{O}_3(g)+6 \mathrm{H}^{+}(a q)+6 \mathrm{~F}^{-}(a q) \end{aligned}$$

Water has the ability to act as an acid as well as base, i.e., it behaves as an amphoteric substance. From the Bronsted Lowry theory, it acts as an acid with $\mathrm{NH}_3$ and a base with $\mathrm{H}_2 \mathrm{~S}$.

$\begin{aligned} & \mathrm{H}_2 \mathrm{O}(l)+\mathrm{NH}_3(\mathrm{aq}) \longrightarrow \mathrm{OH}^{-}(\mathrm{aq})+\mathrm{NH}_4^{+}(\mathrm{aq}) \\ & \mathrm{H}_2 \mathrm{O}(l)+\mathrm{H}_2 \mathrm{~S}(\mathrm{aq}) \longrightarrow \mathrm{H}_3 \mathrm{O}^{+}(\mathrm{aq})+\mathrm{HS}^{-}(a q)\end{aligned}$

The auto - protolysis (self-ionisation) of water takes place. The reaction are as follows

$$\underset{\text { Acid }}{\mathrm{H}_2 \mathrm{O}(l)}+\underset{\text { Base }}{\mathrm{H}_2 \mathrm{O}}(l) \longrightarrow \underset{\begin{array}{c} \text { Conjugate } \\ \text { acid } \end{array}}{\mathrm{H}_3 \mathrm{O}^{+}}(a q)+\underset{\begin{array}{c} \text { Conjugate } \\ \text { base } \end{array}}{\mathrm{OH}^{-}(\mathrm{aq})}$$

A. $\rightarrow(9,10)$

B. $\rightarrow(4,5,7,8,9)$

C. $\rightarrow(6)$

D. $\rightarrow(1,3)$

E. $\rightarrow(2,4)$

F. $\rightarrow(5)$

A. Synthesis gas - Synthesis of methanol

- Mixture of CO and H$$_2$$

$\begin{aligned} \text{B. Dihydrogen }\quad & - \text { Reducing agent } \\ & - \text { Stoichiometric compounds of } s \text {-block elements } \\ & -\mathrm{Zn}+\mathrm{NaOH} \\ & -\mathrm{Zn}+\text { dil. } \mathrm{H}_2 \mathrm{SO}_4 \\ & - \text { Synthesis of methanol }\end{aligned}$

C. Heavy water - Prolonged electrolysis of water

D. Calgon $-\mathrm{Na}_2\left[\mathrm{Na}_4\left(\mathrm{PO}_3\right)_6\right]$

- Softening of water

E. Hydrogen peroxide - Oxidising agent

— Reducing agent

F. Salt like hydrides - Stoichiometric compounds of s-block elements.