(i) H₂O undergoes extensive H-bonding due to high electronegativity of O-atom and hence exist as an associated molecule.
(ii) Therefore H₂O is a liquid. On the other hand H₂O does not undergo H-bonding and hence exists as a discrete molecules and as a gas.

(i) The two O-O bond lengths are identical due to resonance.
(ii) Due to the strong bond formation with other elements.

(i) The given statement is true.
(ii) The relative acidic strength of HF, HCI, HBr and HI depends upon their bond dissociation enthalpies.
(iii) Since, the bond dissociation enthalpy of H-X bond from H-F to H-I as the size of atom increases from F to l. Therefore, the acidic strength increases in the opposite order as:
H - F < H - CI < H - Br < H - I

(i) Ozone acts as a powerful oxidizing agent because ozone liberates nascent oxygen very easily on decomposition.
\({ O }_{ 3 }\longrightarrow { O }_{ 2 }+\left[ O \right] \)
(ii) This nascent or atomic oxygen brings about the oxidations it is very reactive.

(i) HCl < HBr < HI < HF
(ii) Fluorine being the most electronegative element cannot have positive oxidation state. Other halogens have d-orbitals, therefore can expand their octet.

Element of group 15 have stable half-filled p-orbitals hence large amount of energy is required to remove electrons as compared to group 16, which has an incomplete p subshell.

(i) Nitric acid is used as a oxidising agent and in the preparation of aqua regia.
(ii) Salts of nitric acid are used in photography (AgNO₃) and gun powder for fire arms (NaNO₃)·

HF is a weak acid i.e. 0.1 M solution is only 10% ionised, but in 5M & 15M solution, HF is stronger acid due to chemical equilibrium.
\(\mathrm{HF}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{F}^{-}  \)
\(\mathrm{HF}+\mathrm{F}^{-} \rightleftharpoons \mathrm{HF}_{2}^{-}\)

On heating PCl₅, it decomposes into PCl₃ and chlorine.
\(\mathrm{PCl}_{5(\mathrm{~g})} \rightarrow \mathrm{PCl}_{3(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})}\)

Argon prevents the oxidation of hot filament and prolongs the life in filament bulbs.

\(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow 12 \mathrm{C}+\mathrm{H}_{2} \mathrm{SO}_{4} \cdot 11 \mathrm{H}_{2} \mathrm{O} \\ \text { Sucrose } \)
\(\underset{\text { Formic acid }}{\mathrm{HCOOH}}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{CO}+\mathrm{H}_{2} \mathrm{SO}_{4} \cdot \mathrm{H}_{2} \mathrm{O}\)
\(\underset{\text { Oxalic acid }}{\mathrm{(COOH)}_{2}}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{CO}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \cdot \mathrm{H}_{2} \mathrm{O}\)

Chlorine is prepared by the action of conc. sulphuric acid on chlorides in presence of manganese dioxide
4NaCl + MnO₂ + 4H₂SO₄ \(\longrightarrow \)Cl₂+ MnCl₂ +4NaHSO₄ + 2H₂O

(i) The Chalcogens belong to group (16).
(ii) The group consists of elements: Oxygen, Sulphur, Selenium, Tellurium and Polonium.
(iii) These are ore forming elements as most of the ores are oxides and sulphides.
(iv) Chalcos meaning 'ore formers'.

(i) In heavier post transition metals, the outers electrons (ns) have a tendency to remain inert and show reluctance to take part in the bonding, which is known as inert pair effect.
(ii) This effect is also observed in groups 14, 15 and 16.

(i) PCI₅+ C₂H₅OH \(\longrightarrow \) C₂H₅CI + POCl₃ + HCI
(ii) P₄+ 10SO₂Cl₂ \(\longrightarrow \) 4PCI₅ + 10SO₂
(iii) POCl₃ + 3H₂O \(\longrightarrow \) H₃PO₄ + 3HCI
(iv) PH₃ + HBr\(\longrightarrow \) PH₄Br
(v) PCl₃+ 3H₂O\(\longrightarrow \) H₃PO₃ + 3 HCI

(i) All these acids on losing a proton give their corresponding conjugate bases (ie) ClO-,
CIO₂ ^-, CIO₃ - and CIO₄ ^-. Their structures are:

(ii) Since, oxygen is more electronegative than chlorine, therefore dispersal of negative charge present on oxygen atom (Singly bonded to CI) increases as the number of oxygen atoms attached by a double bond: to chlorine increases due to \(P\pi -d\pi \) back bonding.
(iii) Therefore stability of ions will increase in the following order:
CIO- < CIO₂- < CIO₃- < CIO₄-
(iv) Due to increase in stability of conjugate bases, acidic strength of corresponding acid increases in the same order as :
HCIO- < HCIO₂ < HCIO₃ < HCIO₄

(i) The thermal stability of hydrides of group 16 elements is directly proportional to the bond dissociation enthalpy of H- E bond.
(ii) On moving down the group, bond dissociation energy decreases and hence, E- H bond breaks easily.
(iii) Thus, the thermal stability of hydrides of group 16 elements decreases down the group. Hence the order of thermal stability is,
H₂O > H₂S > H₂Se > H₂Te > H₂Po

(i) Fluorine is the most reactive element among halogens due to minimum value of F- F bond dissociation energy.
(ii) It can form two types of salts with metals NaF and NaHF₂
(iii) AgF is soluble in water but other AgX are insoluble.
(iv) HF attacks glass while others do not.
(v) Fluorine, does not form any polyhalides (absence of d - orbitals)
(vi) Fluorine exhibit only negative oxidation state (highly electronegative) while other halogens have both +ve and -ve oxidation state.

(i) Dilute solution of sulphuric acid/aqueous : solution of sulphates gives white precipitate (barium sulphate) with barium chloride solution.
(ii) It can also be detected using lead acetate solution. Here a white precipitate of lead sulphate is obtained
(iii) \({ BaCl }_{ 2 }+{ H }_{ 2 }{ SO }_{ 4 }\longrightarrow { { BaSO }_{ 4 } } \downarrow +2Hcl\)
                                   Barium sulphate (White precipitate)
(iv) \(\left( { CH }_{ 3 }COO \right) _{ 2 }Pb+{ H }_{ 2 }{ SO }_{ 4 }\longrightarrow { PbSO_4 }\downarrow +{ 2CH }_{ 3 }COOH\)
                                                     Lead Sulphate (White precipitate)

Structure of ammonia
(i) Ammonia molecule is pyramidal in shape N-H bond distance is 1.016Å and H-H bond, distance is 1.645Å with a bond angle 107°.

(ii) The structure of ammonia may be regarded as a tetrahedral with one lone pair of electrons in one tetrahedral position hence it has a pyramidal shape.

(i) Sulphuric acid is used in the manufacture of fertilisers, ammonium sulphate and super phosphates and other chemicals such as HCl, HNO₃.
(ii) It is used as a drying agent and also used in the preparation of pigments, explosives etc.

Each halogen combines with other halogens to form a series of compounds are called interhalogen compounds.
Example: AB type: BrF
AB₃ type: ICI₃

(i) As per the position in the periodic table, the element A is phosphorus as below:
(ii) Phosphorus reacts with dry chlorine to form phosphorus trichloride as below
\(\underset { (A) }{ { P }_{ 4 } } +6{ Cl }_{ 2 }\longrightarrow \underset { (B) }{ { 4PCl }_{ 3 } } \)
Hence, compound B is phosphorus trichloride.
(iii) PCl₃ on hydrolysis gives phosphorus acid H₃PO₃, which is dibasic acid,
\(\underset { (B) }{ { PCl }_{ 3 } } +3{ H }_{ 2 }O\longrightarrow { 3HCl }+\underset { (C) }{ { H }_{ 3 }{ PO }_{ 3 } } \)  
Hence, compound C is phosphorus acid.
(iv) H₃PO₃ on heating undergo auto oxidation and reduction producing phosphoric acid md phosphine as below:
\(\underset { (c) }{ { 4H }_{ 3 }{ PO }_{ 3 } } \overset { \Delta }{ \longrightarrow } { PH }_{ 3 }+\underset { (b) }{ { 3H }_{ 3 }{ PO }_{ 4 } } \)
Phosphoric acid is a tribasic acid. Hence, compound D is phosphoric acid.
Thus A = Phosphorus
B = Phosphorus trichloride
C = Phosphorus acid
D = Phosphoric acid

Manufacture of sulphuric acid by contact process:
The contact process involves the following steps.
(i) Initially sulphur dioxide is produced by burning sulphur or iron pyrites in oxygen/ air.
\(S+{ O }_{ 2 }\longrightarrow { SO }_{ 2 }\)
\({ 4FeS }_{ 2 }+{ 11O }_{ 2 }\longrightarrow { 2Fe }_{ 2 }{ { O }_{ 3 } }+8{ SO }_{ 2 }\)
(ii) Sulphur dioxide formed is oxidised to sulphur trioxide by air in the presence of a catalyst such as V₂O₅ or platinised asbestos.
(iii) The sulphur trioxide is absorbed in concentrated sulphuric acid and produces oleum (H₂S₂O₇). The oleum is converted into sulphuric acid by diluting it with water. 
\(\mathrm{SO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7} \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} 2 \mathrm{H}_{2} \mathrm{SO}_{4}\)
(iv) To maximise the yield the plant is operated at 2 bar pressure and 720 K. The sulphuric acid obtained in this process is over 96 % pure.

(i) KCIO₃ \(\overset { \Delta }{ \underset { { MnO }_{ 2 } }{ \longrightarrow } } \) 2KCI + 3O₂
(ii) 2 ZnS + 3O₂\(\longrightarrow \) 2 ZnO + 2 SO₂
(iii) AI_zO₃(s) + 6 NaOH_(aq) + 3 H₂O_(l) \(\longrightarrow \) 2 Na₃[AI(OH)₆]_(aq)
(iv) 2NaOH + SO₂\(\longrightarrow \)Na₂SO₃ + H₂O
(v) 2KCl + H₂SO₄ \(\longrightarrow \) 2 HCl + K₂SO₄

(a) Rhombic Sulphur (α - Sulphur):
(a) It is yellow in colour.
(b) Its melting point is 385.8K and specific gravity is 2.06
(c) It is stable form of sulphur at room temperature.
(d) It is formed on evaporating the solution of sulphur in CS₂.
(e) It in insoluble in water, readily soluble in CS₂ and dissolves to some extent in benzene, alcohol and ether.
(b) Monoclinic sulphur \(\left( \beta -sulphur \right) \):
(a) Its melting point is 393K and specific gravity is 1.98
(b) It is prepared by melting rhombic sulphur in a dish and cooling, till crust is formed. Two holes are made in crust and remaining liquid is powered out. On removing crust, colourless needle - shaped crystals of β - sulphur is formed.
(c) Monoclinic sulphur is stable above 369K and below 369K α - sulphur is stable.
(d) At 369K both forms are stable and this temperature is called transition temperature.
(e) Both rhombic and monoclinic sulphur have S₈ molecules, these are packed to give different crystal structure S₈ form is puckered and has crown shape.
Several other modifications containing 6-20 sulphur atoms per ring are synthesised 

(f) In Cyclo-S₆ the ng adopts chair form.

(g) At elevated temperatures (～1000K), S₂ is dominant species and is, paramagnetic like O₂

Each halogen combines with another halogen to form several compounds known as interhalogen compounds.

AX	AX3	AX3	AX7
CIF	CIF2	BrF5	IF7
ICI	ICl3	IF5

Methods of Preparation interhalogen compounds:
I₂+ Cl₂(equimolar) \(\longrightarrow \)2ICI (AX)
Cl₂ + 3F₂ (Excess) 2CIF₃ (AX₃)
I₂+ 5F₂ (Excess) \(\longrightarrow \) 21F₅(AX₅)
IF₅ + F₂ (Excess)\(\overset { 573K }{ \longrightarrow } \) IF₇ (AX₇)
Structure of interhalogen compounds.
(i) Type AX: These are covalent compounds in which the larger halogen forms the central atom.
Eg: CIF, BrF
AX sp³ hybridisation-linear linear
(ii) Type AX₃:

(a) Without lone pair of electrons, it is T-shaped.
(b) BipyramidaI structure.
(c) sp³ hybridisation. Eg: CIF₃
(iii) Type AX₅:

(a) Without lone pair, it iF square pyramidal
(b) Octahedral structure
(c) sp³d² hybridisation 
Eg: IF₅
(iv) Type AX₇:

(a) Pentagonal pyramidal.
(b) sp³d³ hybridisation Eg: IF₇