Those hydrides which do not have fix composition are called non-stoichiometric hydrides, and the composition varies with temperature and pressure. This type of hydrides are formed by d and f block elements. They cannot be formed by alkali metals because alkali metal hydrides form ionic hydrides.

Atomic hydrogen atoms, produced by dissociation of dihydrogen with the help of an electric arc, are allowed to recombine on the surface to be welded. In this process, a large amount of energy is liberated which is used to generate a temperature of 4000 K for cutting and welding purpose in the form of atomic hydrogen or oxy-hydrogen torches.

Hydrogen is a gas at room temperature. Because of it occupying large volume, it is difficult to transport it either by rail or by road. However, by cooling and applying high pressure, gaseous \({ H }_{ 2 }\) can be converted into liquid \({ H }_{ 2 }\)which has much smaller volume and hence, can be transported easily. Thus, the basic property of hydrogen which is useful for hydrogen economy is that it can be converted into a liquid by cooling under high pressure.

Dilute solutions of \({ H }_{ 2 }{ O }_{ 2 }\)cannot be concentrated by heating because it decomposes much below its boiling point.\(2{ H }_{ 2 }{ O }_{ 2 }\rightarrow { 2H }_{ 2 }O+{ O }_{ 2 }\)

(i) Hydrogen economy: The basic principle of hydrogen economy is the storage and transportation of energy in the form of liquid or gaseous dihydrogen.
(ii) Hydrogenation: Hydrogenation means addition of hydrogen across double and triple bonds in presence of catalyst to form saturated compounds.
Vegetable oil + H₂ \(\overset { Ni,437K }{ \longrightarrow } \) Vegetable Ghee
(iii) Syngas: The mixture of CO and H₂ are called synthesis or syngas. It can be produced by the reaction of steam on hydrocarbon or coke at high temperature in the presence of nickel catalyst
CH₄(g) + H₂O(g) \(\overset { 1270K }{ \underset { Ni }{ \longrightarrow } } \) CO(g) + 3H₂(g)
The process of producing syngas from coal is called 'Coal gasification'.
C(g) + H₂O(g) \(\overset { 1270K }{ \underset { Ni }{ \longrightarrow } } \) CO(g) + H₂(g)
(iv) Water-gas shift reaction: The amount of hydrogen in the syngas can be increased by the action of CO of syngas mixture with steam in the presence of iron chromate as catalyst.
C(s) + H₂O(g) \(\overset { 673K }{ \underset { { FeCrO }_{ 4 } }{ \longrightarrow } } \) CO(g) + H₂(g)
This is called water-gas shift reaction.
(v) Fuel-Cell: It is a cell which converts chemical energy of fuel directly into electrical energy.

Water free from ca²⁺ and Mg²⁺ ions is called soft water.

Yes, because these are unsaturated fats and hence,good for health. They do not form cholesterol if taken in small quantity.

\(2MnO_{ 4 }^{ - }(aq)+{ 5H }_{ 2 }{ O }_{ 2 }(l)+6{ H }^{ + }(aq)\rightarrow 2Mn^{ 2+ }(aq)+8{ H }_{ 2 }O(l)+{ 5O }_{ 2 }(g)\)
(Redox reduction)

The reaction of H₂O₂ with acidified KI Solution.
\(2KI+{ H }_{ 2 }{ SO }_{ 4 }+{ H }_{ 2 }{ O }_{ 2 }\longrightarrow { K }_{ 2 }{ SO }_{ 4 }+{ I }_{ 2 }+2{ H }_{ 2 }O\)
\( 34 \ g \ 254 \ g\)
\( 5 \ { cm }^{ 3 } \ 0.508 \ g\)
\(254 \ g \ af \ { I }_{ 2 } \ is \ liberated \ by \ { H }_{ 2 }{ O }_{ 2 }=34g\)
\(0.508 \ g \ { I }_{ 2 } \ is \ liberated \ by \ { H }_{ 2 }{ O }_{ 2 }=\frac { 34 }{ 254 } \times 0.508=0.068g\)
\(Now,5{ cm }^{ 3 } \ of \ { H }_{ 2 }{ O }_{ 2 } \ contains=0.068g \ of\quad { I }_{ 2 }\)
\(then,1{ cm }^{ 3 } \ of \ { H }_{ 2 }{ O }_{ 2 } \ contains=\frac { 0.068 }{ 5 } =0.0136g \ of \ { I }_{ 2 }\)
\( now,\ 2{ H }_{ 2 }{ O }_{ 2 }\longrightarrow 2{ H }_{ 2 }O+{ O }_{ 2 }\)
\( 68g \ 22400mL \ at \ STP\)
\( 68g \ of \ { H }_{ 2 }{ O }_{ 2 } \ gives \ 22400mL \ { O }_{ 2 } \ at \ STP\)
\(1{ cm }^{ 3 } \ or \ 0.0136g \ of \ { H }_{ 2 }{ O }_{ 2 } \ give \ { O }_{ 2 } \ at \ STP\)
\( =\frac { 22400 }{ 68 } \times 0.0136\)
\( =4.48mL \ of \ STP\)
\( \therefore \ Strength \ of \ { H }_{ 2 }{ O }_{ 2 }=4.48 \ volumes\)

Water is amphoteric in nature because it acts as an acid
\(\underset { Base \ 1 }{ { H }_{ 2 }O(l) } +\underset { Acid\ 2 }{ { H }_{ 2 }S(aq) } \longrightarrow \underset { Acid \ 1 }{ { H }_{ 3 }{ O }^{ + }(aq) } +\underset { Base \ 2 }{ { HS }^{ - }(aq) } \)
\(\underset { Acid \ 1 }{ { H }_{ 2 }O(l) } +\underset { Base \ 2 }{ { NH }_{ 3 }(aq) } \longrightarrow \underset { Acid \ 2 }{ { NH }_{ 4 }^{ + }(aq) } +\underset { Base \ 1 }{ { OH }^{ - }(aq) } \)

(i) Electron deficient hydrides: Compounds in which central atom has incomplete octet, are called electron deficient hydrides. For example, BeH₂, BH₃ are electron deficient hydrides.
(ii) Electron precise hydrides: Those compounds in which exact number of electrons are present in central atom or the central atom contains complete octet are called precise hydrides e.g., CH₄, SiH₄, GeH₄ etc. are precise hydrides.
(iii) Electron rich hydrides: Those compounds in which central atom has one or more lone pair of excess electrons are called electron rich hydrides" e.g., NH₃, H₂O.

Given, degree of hardness = 46ppm
Which menas that 10⁶ g of sample require 46g of CaCo₃
CaCO₃ present in 1000g of water = \(\frac { 46\times 1000 }{ 10^{ 6 } } \)
= 46 x 10^-3g
1 mol (or 100g) of CaCO₃= 1 mol (or 120g) of MgSO₄
46 x 10^-3 g of CaCo₃ = \(\frac { 120\times 46\times 10^{ -3 } }{ 100 } \)g
= 0.055 g or 55 mg

100 mL of \({ H }_{ 2 }O_{ 2 }\)solution contains \({ H }_{ 2 }O_{ 2 }\) = 3g
\(\therefore \)1000 mL of \({ H }_{ 2 }O_{ 2 }\)solution will contains
\({ H }_{ 2 }O_{ 2 }=\frac { 3 }{ 100 } \times 1000=30g\)
Consider the chemical equation,
\(\underset { 2\times34 \ = \ 68g }{ 2H_{ 2 }{ O }_{ 2 } } \rightarrow \underset { 22.7 \ L \ at \ NTP }{ { 2H }_{ 2 }{ O }+{ O }_{ 2 } } \)
Now 68 g of \({ H }_{ 2 }{ O }_{ 2 }\) gives \({ O }_{ 2 }\)at NTP = 22.7 L
\(\therefore \)30 g of \({ H }_{ 2 }O_{ 2 }\)will give \(O_{ 2 }\)at NTP = \(\frac { 22.7 }{ 68 } \times30\approx 10.014\)
But 30g of \({ H }_{ 2 }O_{ 2 }\) are present in 1000 mL of \({ H }_{ 2 }O_{ 2 }\)
Hence, 1000mL of \({ H }_{ 2 }O_{ 2 }\) solution gives \(O_{ 2 }\)at NTP
\(=\frac { 10014 }{ 1000 } =10.01mL\)
Hence, the volume strength of 3%\({ H }_{ 2 }{ O }_{ 2 }\) solution = 10.01

Reaction with chlorine when dihydrogen combines with chlorine, it reduces it to the chloride ion (Cl^-) and itself get oxidised to H⁺ ion, to give hydrogen chloride, a covalent compound formed by sharing of a pair of electrons between H and Cl.
\({ H }_{ 2 }(g)+{ Cl }_{ 2 }(g)\rightarrow 2HCl(g)\)