\('A'\quad is\quad { S }_{ 8 }.\quad 'B'is{ SO }_{ 2 }(g).\)
\({ S }_{ 8 }+{ 8O }_{ 2 }\overset { heat }{ \rightarrow } { 8SO }_{ 2 }(g)\)
'B' decolorizes \(KMnS{ O }_{ 4 }\) 
\(2KMn{ O }_{ 4 }+5S{ O }_{ 2 }+{ 2H }_{ 2 }O\longrightarrow { 2H }_{ 2 }{ SO }_{ 4 }+2Mn{ SO }_{ 4 }+{ K }_{ 2 }{ SO }_{ 4 }\)
'B' turns lime water milky due to formation of  
\(Ca{ (OH) }_{ 2 }(aq)+{ SO }_{ 2 }(g)\longrightarrow CaSO_{ 3 }(s)+{ H }_{ 2 }O(l)\)
'B' is obtained by roasting of sulphideores
\(2ZnS(s)+{ 3O }_{ 2 }\longrightarrow 2ZnO(s)+{ 2SO }_{ 2 }(g)\)
 'B' reduces in aqueous solution.
\(2{ Fe }^{ 3+ }+{ SO }_{ 2 }+{ 2H }_{ 2 }O\longrightarrow { Fe }^{ 2+ }+{ SO }_{ 4 }^{ 2- }+{ 4H }^{ + }\)

(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.

\({ P }_{ 4 }={ 6CI }_{ 2 }\longrightarrow { 4PCI }_{ 3 }\)
\(\left[ { PCI }_{ 3 }+{ 6H }_{ 2 }O\longrightarrow { H }_{ 3 }{ PO }_{ 3 }+3HCI \right] \times 4\)
\({ P }_{ 4 }+{ 6CI }_{ 2 }+{ 12H }_{ 2 }O\longrightarrow { 4H }_{ 3 }{ PO }_{ 3 }+{ 12HCI }\)
1 mole of white phosphorus produces 12 moles of HCI.
\(\frac { 62 }{ 124 }\)mole of white phosphorus produces \(12\times \frac { 62 }{ 124 } =6\)moles of HCI.
Mass of 6 moles of HCI= 6 X 36.5
= 219.0 g of HCI.

P₄O₆ + 6H₂O \(\to\) 4H₃PO3
\(\left[ { H }_{ 3 }{ PO }_{ 3 }+2HaOH\longrightarrow { Na }_{ 2 }HPO_{ 3 }+{ 2H }_{ 2 }O \right] \times 4\) 
\({ P }_{ 4 }{ O }_{ 6 }+8NaOH\longrightarrow { 4Na }_{ 2 }{ HPO }_{ 4 }+{ 2H }_{ 2 }O\)
1 mole P₄O₆ is neutralised by \(8\times \frac { 1.1 }{ 220 } =\frac { 8 }{ 200 } =0.04\)
Volume of 0.1 M NaOH need 0.1 x in L=0.04 mol
\({ V }_{ 1 }=\frac { 0.04 }{ 0.1 } =0.4\)  Litre = 400ml of NaOH

'A' is PCl_5. (It is a yellowish-white solid).
'B' is PCl₃ (It is a colourless oily liquid).
P₄(s) + 10Cl₂(g) \(\to\) 4PCl₅(s)
P₄(s) + 6Cl₂ (g) \(\to\) 4PCI₃(l)
PCl₅, on hydrolysis gives H₃PO₄, whereas
PCl₃, on hydrolysis gives H₃PO₃.
PCl₅ + 4H₂O \(\to\) H₃PO₄ + 5HCl
PCl₃ + 3H₂O \(\to\) H₃PO₃ + 3HCl

(i) F₂ > Cl₂ > Br₂ > I₂ is decreasing order of oxidising power.
(ii) HI > HBr > HCl > HF is decreasing order of strength of acid.
(iii) HClO > HClO₂ > HCIO₃ > HCIO₄ is order of oxidising power.
HOI > HOBr > HOCl is order of oxidising power>
HOF does not exist at room temperature.

(a) It is due to presence of unpaired electrons in vapour state in S₂ like in O_2.
(b) HF has more bond dissociation energy than HCl due to smaller bond length.
(c) NH₃ is more basic than PH₃ due to smaller size of nitrogen, therefore, NH₃ has more proton affinity than PH₃ .  Lone pair of electrons is more available on nitrogen than phosphorous.

(i) It is because ionisation enthalpy of Bi is lower than phosphorus, therefore, Bi forms ionic BiCl₃; whereas PCl₃ is covalent.
(ii) It is because O₃ is highly unstable and gives out [O] due to which it is powerful oxidising agent.
(iii) It is because F₂ has highest standard reduction potential, higher than Cl₂.