Match the items in Column I with the relevant item in Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | Hydrogen peroxide is used as a | 1. | zeolite |
| B. | Used in Calgon method | 2. | perohydrol |
| C. | Permanent hardness of hard water is removed by | 3. | sodium hexametaphosphate |
| 4. | propellant |
A. $\rightarrow(2,4)$
B. $\rightarrow$ (3)
C. $\rightarrow(1,3)$
A. Hydrogen peroxide is used as a perhydrol and propellant.
B. Sodium hexametaphosphate is used in Calgon method.
C. Permanent hardness of hard water is removed by zeolite and sodium hexametaphosphate.
Assertion (A) Permanent hardness of water is removed by treatment with washing soda.
Reason (R) Washing soda reacts with soluble magnesium and calcium sulphate to form insoluble carbonates.
Assertion (A) Some metals like platinum and palladium, can be used as storage media for hydrogen.
Reason (R) Platinum and palladium can absorb large volumes of hydrogen.
Atomic hydrogen combines with almost all elements but molecular hydrogen does not. Explain.
Atomic hydrogen is highly unstable. Since, the electronic configuration of atomic hydrogen is $1 s^1$, it needs one more electron to complete its configuration and gain stability. Therefore, atomic hydrogen is very reactive and combines with almost all the elements.
It, however, reacts in three different ways i.e.,
(i) by loss of its single electron to form $\mathrm{H}^{+}$,
(ii) by gain of one electron to form $\mathrm{H}^{-}$ and
(iii) by sharing its electron with other atoms to form single covalent bonds. In contrast, the bond dissociation energy form $\mathrm{H}-\mathrm{H}$ bond is very high ( $435.88 \mathrm{~kJ} \mathrm{~mol}^{-1}$ ). As a result, molecular hydrogen is almost inert at room temperature and hence reacts only with a few elements.
How can $\mathrm{D}_2 \mathrm{O}$ be prepared from water? Mention the physical properties in which $\mathrm{D}_2 \mathrm{O}$ differs from $\mathrm{H}_2 \mathrm{O}$. Give at least three reactions of $\mathrm{D}_2 \mathrm{O}$ showing the exchange of hydrogen with deuterium.
(i) $\mathrm{D}_2 \mathrm{O}$ can be prepared by prolonged electrolysis of water.
(ii) Physical properties
(a) $\mathrm{D}_2 \mathrm{O}$ is colourless, odourless, tasteless liquid. It has maximum density $-1.1073 \mathrm{~g} \mathrm{~mL}^{-1}$ at $11.6^{\circ} \mathrm{C}$ (Maximum density of water at $4^{\circ} \mathrm{C}$ ).
(b) Solubility of salts in heavy water is less than in ordinary water because it is more viscous than ordinary water.
(c) Nearly, all physical constants of $\mathrm{D}_2 \mathrm{O}$ are higher than $\mathrm{H}_2 \mathrm{O}$. It is due to the greater nuclear mass of deuterium atom than H -atom and stronger H -bonding in $\mathrm{D}_2 \mathrm{O}$ than $\mathrm{H}_2 \mathrm{O}$.
(iii) Exchange reactions of hydrogen with deuterium
$\begin{aligned} \mathrm{NaOH}+\mathrm{D}_2 \mathrm{O} & \longrightarrow \mathrm{NaOD}+\mathrm{HOD} \\ \mathrm{HCl}+\mathrm{D}_2 \mathrm{O} & \longrightarrow \mathrm{DCl}+\mathrm{HOD} \\ \mathrm{NH}_4 \mathrm{Cl}+\mathrm{D}_2 \mathrm{O} & \longrightarrow \mathrm{NH}_3 \mathrm{DCl}+\mathrm{HOD}\end{aligned}$