(i) High pressure (2 bar),
(ii) 720 K temperature,
(iii) V₂O₅ as catalyst.

\({ P }_{ 4 }{ O }_{ 10 }\) is a strong dehydrating agent. It reacts with \({ HNO }_{ 3 }\) to form metaphosphoric acid  \(\left( { HPO }_{ 3 } \right) \) and dinitrogen pentoxide, \({ N }_{ 2 }{ O }_{ 5 }\) 
\(4HN{ O }_{ 3 }+{ P }_{ 4 }{ O }_{ 10 }\longrightarrow 4HP{ O }_{ 3 }+2{ N }_{ 2 }{ O }_{ 5 }\)     \(\) 

(i) \(Xe +\underset {excess} {2F_{2}} \xrightarrow [7 bar] {873 k} XeF_{4}\) 
(ii) \(6Li + N_{2} \rightarrow 2Li_{3}N\)

\(\)

(i) It is because bond dissociation energy of H-O bond is highest as compared to H-E bond where 'E' is group 16 element.
(ii) It is because white phosphorus is monomeric and has less bond dissocation enthalpy whereas red phosphorus is polymeric.

(i) It is because F₂ is stronger oxidising agent than CL₂, therefore NF₃ is exothermic compound whereas NCL₃ is endothermic.
(ii) In SF₄, bonds are in different planes, therefore, they are not equivalent.

(a) White phosphorus exists as discrete (separate) tetrahedral molecules. Thus, it has tetrahedral structure with six P-P bonds. Red phosphorus has polymeric  structure in which   molecules (tetrahedral) are linked through P-P bonds to form chain. Black phosphorus has two forms -black and -black phosphorus. It can be sublined in air and has opaque monoclinic or rhomohedral crystals; It does not oxidise in air. -black phosphorus does not burn in air up to 673 K. Black phosphorus is thermodynamically most stable.
Reactivity: White phosphorus is more reactive than red phosphorus because it is monomeric and has angular strain due to bond angles at 60°C. Black phosphorus is also less reactive.

(i) \({ NH }_{ 4 }{ NO }_{ 2 }(s)\underrightarrow { heat } { N }_{ 2 }+{ 2H }_{ 2 }O\) 
                'A'                 'B'
(ii) \({ N }_{ 2 }+{ 3H }_{ 2 }\longrightarrow 2{ NH }_{ 3 }(g)\) 
                              'C' basic
(iii) \({ 4NH }_{ 3 }+{ 5O }_{ 2 }\longrightarrow 4NO+{ 6H }_{ 2 }O\) 
\(\\ 2NO+{ O }_{ 2 }\longrightarrow { 2NO }_{ 2 }\) 
                  'D' (part of acid rain)
\({ 3NO }_{ 2 }+{ H }_{ 2 }O\longrightarrow 2{ HNO }_{ 3 }+NO\)      

(a)\((i)\quad { 2I }^{ - }+{ O }_{ 3 }+{ H }_{ 2 }{ O }\longrightarrow { I }_{ 2 }+{ O }_{ 2 }+2{ OH }^{ - }\)
\(\\ (ii)\quad { P }_{ 4 }(s)+3NaOH(aq)+{ 3H }_{ 2 }{ O }(l)\longrightarrow { PH }_{ 3 }{ (g) }+{ 3NaH }_{ 2 }{ PO }_{ 2 }\)
(b)(i) It is because bond dissociation energy of H-Te bond is less than H-S bond due to longer bond length.
(ii) It is due to higher standard reduction potential, low bond dissociation energy, high electron affinity and higher enthalpy of hydration.
(iii) It is due to stable electronic configuration i.e., their octet is complete except in He which has duplet i.e., 1st shell is complete having 2 electrons.