Hydrogen Questions in English

$H_2O$: Covalent or molecular hydride (electron-rich hydride).
$B_2H_6$: Covalent or molecular hydride (electron-deficient hydride).
$NaH$: Ionic or saline hydride.

(N/A) Molecular hydrides are classified based on the relative number of electrons and bonds in their Lewis structures as follows:
$(i)$ Electron-deficient hydrides: These hydrides contain fewer than eight electrons around the central atom.
$\rightarrow$ Group-$13$ elements form these hydrides. Examples: $BH_{3}$,$AlH_{3}$.
- These hydrides act as Lewis acids.
$(ii)$ Electron-precise hydrides: In these hydrides,the central atom has exactly eight electrons. Group-$14$ elements form these hydrides. Examples: $CH_{4}$,$SiH_{4}$.
$(iii)$ Electron-rich hydrides: In these hydrides,the central atom has lone pairs of electrons,resulting in more than $8$ electrons in the valence shell. Group-$15$,$16$,and $17$ elements form these hydrides. Examples: $NH_{3}$,$H_{2}O$.

(N/A) Water gas is prepared by passing steam over hot coke at high temperatures. The mixture of $CO$ and $H_{2}$ produced is known as water gas or synthesis gas.
$C_{(s)} + H_{2}O_{(g)} \xrightarrow{1273 \ K} CO_{(g)} + H_{2(g)}$
Producer gas is prepared by passing air over hot coke. The mixture of $CO$ and $N_{2}$ produced is called producer gas.
$2C_{(s)} + O_{2(g)} + 4N_{2(g)} \xrightarrow{1273 \ K} 2CO_{(g)} + 4N_{2(g)}$

(N/A) $LiBH_4$ and $NaBH_4$ are primarily used as selective reducing agents in organic synthesis. They are also used as precursors for the preparation of other metal borohydrides.

(B) Methane reacts with steam at $1270 \ K$ in the presence of a nickel catalyst to produce carbon monoxide and dihydrogen.
This mixture of $CO$ and $H_2$ is known as water gas or syngas.
The balanced chemical equation is:
$CH_{4(g)} + H_2O_{(g)} \xrightarrow[1270 \ K]{Ni} CO_{(g)} + 3H_{2(g)}$

(A) The reaction $CO_2 + 2H_2 \xrightarrow{Cu/ZnO-Cr_2O_3} CH_3OH$ is a catalytic hydrogenation process used for the production of methanol.
The catalyst $Cu/ZnO-Cr_2O_3$ is specifically employed for this industrial conversion.

(N/A) Protium: Symbol: ${ }_{1}^{1} H$,Abundance: $(99.985 \%)$
Deuterium: Symbol: ${ }_{1}^{2} D$,Abundance: $(0.015 \%)$

(N/A) Hydrogen has three isotopes: Protium $(_{1}^{1}H)$,Deuterium ($_{1}^{2}D$ or $_{1}^{2}H$),and Tritium ($_{1}^{3}T$ or $_{1}^{3}H$).

Isotope	Composition $(p, e, n)$
$Protium$ $(_{1}^{1}H)$	$1$ proton,$1$ electron,$0$ neutron
$Deuterium$ $(_{1}^{2}D)$	$1$ proton,$1$ electron,$1$ neutron
$Tritium$ $(_{1}^{3}T)$	$1$ proton,$1$ electron,$2$ neutrons

(A) The common isotope of $Hydrogen$ $(^1H)$ consists of only one proton and one electron. It does not contain any neutrons in its nucleus.

(A) The extraction of glue from bones involves the removal of mineral matter (calcium phosphate) from the bones. This is achieved by treating the bones with dilute $HCl$. The process is known as demineralization.

(B) Producer gas is a mixture of carbon monoxide $(CO)$ and nitrogen $(N_2)$. It is prepared by passing air over red-hot coke at approximately $1273 \ K$. The reaction is as follows:
$2C_{(s)} + O_{2_{(g)}} + 4N_{2_{(g)}} \xrightarrow{1273 \ K} 2CO_{(g)} + 4N_{2_{(g)}}$

(B) The preparation of water gas, also known as syngas, involves the reaction of coke with steam at high temperatures $(473 - 1273 \ K)$:
$C_{(s)} + H_2O_{(g)} \xrightarrow{473 - 1273 \ K} CO_{(g)} + H_{2(g)}$
This mixture of $CO$ and $H_2$ is called water gas or syngas.

(N/A) Beryllium hydride $(BeH_2)$ cannot be prepared directly by the reaction of beryllium with $H_2$. It is prepared by reacting $BeCl_2$ with lithium aluminium hydride $(LiAlH_4)$.
First,$LiAlH_4$ is prepared from lithium hydride $(LiH)$:
$8 LiH + Al_2Cl_6 \rightarrow 2 LiAlH_4 + 6 LiCl$
Then,$BeH_2$ is prepared by the reaction:
$2 BeCl_2 + LiAlH_4 \rightarrow 2 BeH_2 + LiCl + AlCl_3$

(N/A) In the modern periodic table,hydrogen is placed at the top of Group $1$ (alkali metals) because it has $1$ electron in its valence shell $(1s^1)$.
However,hydrogen also shows properties similar to halogens (Group $17$) as it requires only $1$ electron to complete its valence shell.
Due to this dual nature,its position is considered unique and is often placed separately at the top of the periodic table.

(N/A) The isotope of hydrogen which contains one proton and one neutron is deuterium $(D)$.
When dideuterium $(D_2)$ reacts with dioxygen $(O_2)$,the product formed is deuterium oxide $(D_2O)$,also known as heavy water.
The chemical equation is: $2D_{2(g)} + O_{2(g)} \xrightarrow{\Delta} 2D_2O_{(l)}$.
The reactivity of $H_2$ and $D_2$ towards oxygen is not the same.
This is because the $D-D$ bond is stronger than the $H-H$ bond due to the higher mass of deuterium,which leads to a lower zero-point energy.
Consequently,$H_2$ is more reactive than $D_2$ towards oxygen.

(N/A) Hydrogen resembles alkali metals,i.e.,$Li, Na, K, Rb, Cs$,and $Fr$ of group $1$ of the periodic table in the following respects:
$(i)$ Like alkali metals,hydrogen contains one electron in its outermost orbit and exhibits a $+1$ oxidation state.
$(ii)$ Like alkali metals,hydrogen loses its only electron to form a positive ion,i.e.,$H^+$.
$(iii)$ Like alkali metals,hydrogen combines with electronegative elements such as oxygen,halogens,and sulphur to form oxides,halides,and sulphides,respectively.
$(iv)$ Like alkali metals,hydrogen acts as a strong reducing agent.

(N/A) Hydrogen has one electron in its $1s$ orbital. To achieve the stable noble gas configuration of helium $(1s^2)$,it can either lose,gain,or share this electron.
However,the ionization enthalpy of hydrogen is very high $(1312 \ kJ \ mol^{-1})$,making it difficult to lose an electron to form an $H^+$ ion.
Conversely,its electron gain enthalpy is only slightly negative $(-73 \ kJ \ mol^{-1})$,meaning it does not have a strong tendency to gain an electron to form an $H^-$ ion.
Due to these energetic factors,hydrogen prefers to share its electron with other non-metals to form covalent bonds.

(N/A) The primary property of hydrogen useful for the hydrogen economy is its ability to be liquefied under high pressure and low temperature. Hydrogen is a gas at room temperature,which makes it difficult to transport in bulk due to its low density. By cooling it and applying high pressure,gaseous $H_2$ can be converted into liquid $H_2$,which occupies a much smaller volume and can be transported easily. The process is a physical change: $H_{2(g)} \xrightarrow[\text{high pressure}]{\text{cooling}} H_{2(l)}$.

(N/A) Atomic hydrogen is highly unstable and hence it is very reactive. Its electronic configuration is $1s^1$. For stability,it tends to complete its shell by gaining,losing,or sharing an electron,making it highly reactive towards almost all elements.
Atomic hydrogen forms hydrides in three ways:
$(i)$ By losing one electron to form $H^+$.
$(ii)$ By gaining one electron to form $H^-$.
$(iii)$ By sharing one electron to form a covalent bond.
In contrast,molecular hydrogen $(H_2)$ has a very high bond dissociation energy of $435.88 \ kJ \ mol^{-1}$. As a result,the $H-H$ bond is strong and stable,making molecular hydrogen relatively inert at room temperature,reacting only with a few elements.

(N/A) $D_2O$ (heavy water) is prepared by the prolonged electrolysis of water,as $H_2O$ is electrolyzed faster than $D_2O$.
Physical properties in which $D_2O$ differs from $H_2O$:
$(i)$ Density: The maximum density of $D_2O$ is $1.1073 \ g \ mL^{-1}$ at $11.6^{\circ}C$,whereas for $H_2O$ it is $1.0000 \ g \ mL^{-1}$ at $4^{\circ}C$.
$(ii)$ Viscosity: $D_2O$ has higher viscosity than $H_2O$.
$(iii)$ Solubility: Salts are generally less soluble in $D_2O$ compared to $H_2O$.
Exchange reactions of hydrogen with deuterium:
$NaOH + D_2O \longrightarrow NaOD + HOD$
$HCl + D_2O \longrightarrow DCl + HOD$
$NH_4Cl + 4D_2O \longrightarrow ND_4Cl + 4HOD$

(N/A) Sodium reacts with dihydrogen to form sodium hydride $(NaH)$,which is a crystalline ionic solid.
$2 Na(s) + H_{2}(g) \rightarrow 2 NaH(s)$
It reacts violently with water to produce dihydrogen gas:
$NaH(s) + H_{2}O(l) \rightarrow NaOH(aq) + H_{2}(g)$
Although $NaH$ does not conduct electricity in the solid state,the electrolysis of its melt produces $H_{2}$ gas at the anode and $Na$ metal at the cathode:
$2 NaH(l) \xrightarrow{\text{Electrolysis}} 2 Na(l) + H_{2}(g)$
At cathode: $Na^{+} + e^{-} \rightarrow Na$
At anode: $2 H^{-} \rightarrow H_{2} + 2 e^{-}$

(C) Anhydrous calcium chloride $(CaCl_2)$ is a strong hygroscopic substance.
It absorbs moisture from the atmosphere without dissolving in it to form a solution,which is a characteristic property of hygroscopic compounds.

(B) $H_{2}O$ exhibits strong intermolecular hydrogen bonding,which leads to a significantly higher boiling point $(373\,K)$.
$H_{2}S$ does not exhibit hydrogen bonding and relies only on weak van der Waals forces.
Therefore,the boiling point of $H_{2}S$ is much lower,approximately $213\,K$,which is less than $300\,K$.

(C) The water-gas reaction (also known as the coal gasification reaction) involves the reaction of carbon with steam at high temperatures to produce a mixture of carbon monoxide and hydrogen,known as water gas or syngas.
The correct equation is: $C_{(s)} + H_2O_{(g)} \xrightarrow{1270 \ K} CO_{(g)} + H_{2(g)}$.

(A) High purity $(>99.95 \%)$ dihydrogen is obtained by the electrolysis of warm aqueous barium hydroxide solution between nickel electrodes.

(D) Hydrazoic acid $(HN_3)$ decomposes upon heating to form hydrogen gas and nitrogen gas.
The balanced chemical equation is:
$2HN_3 \xrightarrow{\Delta} H_2 + 3N_2$

(D) An equimolar mixture of $CO$ and $H_{2}$ is obtained when steam is passed over red hot coke. This mixture is commonly known as synthesis gas or $syn \ gas$.
The reaction is:
$H_{2}O_{(g)} + C_{(s)} \rightarrow CO_{(g)} + H_{2(g)}$

(D) Assertion $A$ is true because hydrogen is indeed the most abundant element in the universe,but nitrogen $(N_2)$ is the most abundant gas in the Earth's troposphere.
Reason $R$ is true because hydrogen is the lightest element with atomic number $Z = 1$.
However,the fact that hydrogen is the lightest element is not the reason why it is not the most abundant gas in the troposphere. The low abundance of hydrogen in the atmosphere is due to its low density and high reactivity,which allows it to escape the Earth's gravitational pull.
Therefore,both $A$ and $R$ are true,but $R$ is not the correct explanation of $A$.

(B) Tritium $\left({ }_{1}^{3} H \right)$ is a radioactive isotope of hydrogen.
It undergoes $\beta^{-}$ decay to form Helium-$3$ according to the reaction: ${ }_{1}^{3} H \rightarrow { }_{2}^{3} He + { }_{-1}^{0} e + \bar{\nu}$.
This process involves the conversion of a neutron into a proton,emitting a low-energy $\beta^{-}$ particle.

(D) Assertion $(A)$ is true because heavy water $(D_2O)$ is commonly used as a tracer in studying reaction mechanisms.
Reason $(R)$ is false because the $O-H$ bond is weaker than the $O-D$ bond due to the kinetic isotope effect. Consequently,the rate of cleavage of the $O-H$ bond is faster than that of the $O-D$ bond,not slower.
Therefore,$(A)$ is true but $(R)$ is false.

(A) The bond dissociation energy of $D_2$ is greater than $H_2$ due to the stronger $D-D$ bond compared to the $H-H$ bond.
Consequently,$D_2$ reacts slower than $H_2$ in chemical reactions.

(D) The process of producing syn-gas from coal is known as coal gasification.
Syn-gas (also known as synthesis gas) is a mixture of $CO$ and $H_2$ in a $1 : 1$ molar ratio.
Since both statements are factually correct,the correct option is $D$.

(B) Atomic hydrogen is produced at high temperature in an electric arc or under ultraviolet radiations.
The dissociation of dihydrogen at $2000 \ K$ is only $0.081 \ \%$,not $8.1 \ \%$.
$H-H$ bond dissociation enthalpy is the highest for a single bond among any diatomic molecule.
Dihydrogen can be produced on reacting $Zn$ with dilute $HCl$ as well as $NaOH_{(aq)}$.

(C) According to $NCERT$,the largest industrial application of dihydrogen is in the synthesis of ammonia $(NH_3)$ by the Haber process.
This ammonia is primarily used for the production of nitrogenous fertilizers.

(D) Among the isotopes of hydrogen,tritium ($^{3}H$ or $T$) is radioactive in nature.
It undergoes $\beta^{-}$-decay to form helium-$3$ $(^{3}He)$.
The reaction is: $^{3}_{1}H \rightarrow ^{3}_{2}He + ^{0}_{-1}e$.
The half-life $(t_{1/2})$ of tritium is approximately $12.33 \ years$,which satisfies the condition of being $> 12 \ years$.

(D) The enthalpy of bond dissociation at $298.2 \ K$ for hydrogen $(H_2)$ is approximately $435.88 \ kJ \ mol^{-1}$.
The enthalpy of bond dissociation at $298.2 \ K$ for deuterium $(D_2)$ is approximately $443.35 \ kJ \ mol^{-1}$.
Comparing these values,we find that $E_{H} \approx 435.88$ and $E_{D} \approx 443.35$.
Calculating the difference: $E_{D} - E_{H} = 443.35 - 435.88 = 7.47 \ kJ \ mol^{-1} \approx 7.5 \ kJ \ mol^{-1}$.
Therefore,the relationship is $E_{H} \simeq E_{D} - 7.5$.

(C) Transition metals of group $7, 8,$ and $9$ do not form hydrides. This is known as the hydride gap.
Among the given options,$Fe$ (group $8$),$Mn$ (group $7$),and $Co$ (group $9$) belong to the hydride gap.
$Cr$ (group $6$) does not fall into this gap and can form interstitial hydrides.

(B) The radioactive isotope of hydrogen is Tritium,represented as ${}_{1}^{3}H$ or ${}_{1}^{3}T$.
For any atom,the number of protons is equal to the atomic number $(Z = 1)$.
Since the atom is neutral,the number of electrons is equal to the number of protons,which is $1$.
The number of neutrons is calculated as $A - Z$,where $A$ is the mass number $(3)$ and $Z$ is the atomic number $(1)$.
Number of neutrons $= 3 - 1 = 2$.
Therefore,the number of neutrons and electrons are $2$ and $1$,respectively.

(D) $1$. $MgH_2$ is an ionic hydride.
$2$. $GeH_4$ is an electron-precise hydride (has $8$ electrons in the valence shell,no lone pairs).
$3$. $B_2H_6$ is an electron-deficient hydride (has less than $8$ electrons in the valence shell).
$4$. $HF$ is an electron-rich hydride (has $8$ electrons in the valence shell with lone pairs).
Therefore,the correct matching is: $a-iv, b-i, c-ii, d-iii$.

(B) The highest industrial consumption of molecular hydrogen is in the Haber process for the production of ammonia $(NH_3)$.
Around $55 \, \%$ of the global hydrogen production is utilized for the synthesis of ammonia by reacting it with nitrogen.

(D) Isotopes are atoms of the same element that have the same atomic number (number of protons and electrons) but different mass numbers due to a different number of neutrons in their nuclei.
Since mass number is the sum of protons and neutrons,a difference in the number of neutrons leads to a difference in atomic mass.

(B) The reaction between dihydrogen $(H_{2})$ and copper$(II)$ oxide $(CuO)$ is a redox reaction where $H_{2}$ acts as a reducing agent.
$CuO(s) + H_{2}(g) \xrightarrow{\Delta} Cu(s) + H_{2}O(l)$
Thus,$CuO$ is reduced to metallic copper $(Cu)$.

(C) High purity $(>99.95\,\%)$ dihydrogen is obtained by the electrolysis of warm aqueous $Ba(OH)_2$ solution between nickel electrodes.

(C) The correct option is $(C)$.
The water-gas shift reaction is represented as: $CO(g) + H_2O(g) \xrightarrow{FeO.Cr_2O_3} CO_2(g) + H_2(g)$.
In this reaction,carbon monoxide $(CO)$ reacts with steam $(H_2O)$ to produce carbon dioxide $(CO_2)$ and hydrogen gas $(H_2)$.

(D) $A-IV, B-III, C-II, D-I$
$A.$ Cobalt catalyst is used in the production of methanol from syngas: $CO + 2H_2 \xrightarrow{Co} CH_3OH$.
$B.$ Syngas is produced by coal gasification: $C_{(s)} + H_2O_{(g)} \rightarrow CO_{(g)} + H_{2(g)}$.
$C.$ Nickel catalyst is used in the production of water gas from hydrocarbons (steam reforming): $CH_{4(g)} + H_2O_{(g)} \xrightarrow{Ni} CO_{(g)} + 3H_{2(g)}$.
$D.$ Electrolysis of brine solution ($NaCl$ solution) produces $H_2$ and $Cl_2$ gases.

(C) Hydrogen can be stored in tanks in the form of metal hydrides.
$NaNi_5$ is a well-known intermetallic compound used for the storage of hydrogen because it can absorb and release hydrogen efficiently at moderate temperatures and pressures.
Therefore,$NaNi_5$ enhances the efficiency of hydrogen storage tanks.

(D) Statement-$I$ is correct.
$Ni$ is used as a catalyst in the hydrogenation of oils to produce edible fats.
Statement-$II$ is incorrect because silicon forms electron-precise hydrides (e.g.,$SiH_4$),not electron-rich or electron-deficient hydrides.

(B) Assertion $A$ is true because the combustion of hydrogen produces only water $(H_2O)$ as a byproduct,making it an environment-friendly fuel.
Reason $R$ is also true because the atomic number of hydrogen is $1$ and it is indeed a very light element.
However,the fact that hydrogen is a light element with atomic number $1$ is not the reason why it is environment-friendly; its environment-friendly nature is due to the clean combustion product $(H_2O)$.
Therefore,both $A$ and $R$ are true,but $R$ is not the correct explanation of $A$.

(B) Atomic hydrogen welding is a process that uses an electric arc between two tungsten electrodes in an atmosphere of hydrogen gas. The hydrogen molecules dissociate into atoms in the arc,absorbing a large amount of heat. When these atoms recombine on the surface of the metal,they release this energy,producing temperatures up to $4000 \ K$,which is sufficient to weld metals with high melting points.