(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)·

a) BrF₅

Valence electron of bromine atom 7+ Number of fluorine atom (5) = 12
\(X=\frac{12}{2}=6\) 
Hybridization: sp³d² ;
Geometry: Square Pyramidal
b) BrF₃

Valence electron of bromine atom 7+ Number of fluorine atom (3) = 10 
X = \(\frac{10}{2}=5\)
Hybridization: sp³d²;
Geometry: Triangular bipyramidal (T - shaped)

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

Thermal stability:
\(4 \mathrm{PH}_{3} \stackrel{317 \mathrm{~K}}{\longrightarrow} \mathrm{P}_{4}+6 \mathrm{H}_{2} \)
Combustion:
\(4 \mathrm{PH}_{3}+8 \mathrm{O}_{2} \stackrel{\Delta}{\longrightarrow} \underset{\text { Phosphorus pentoxide }}{\mathrm{P}_{4} \mathrm{O}_{10}+6 \mathrm{H}_{2} \mathrm{O}} \)
\(\mathrm{P}_{4} \mathrm{O}_{10}+6 \mathrm{H}_{2} \mathrm{O} \stackrel{\Delta}{\longrightarrow} 4 \mathrm{HPO}_{3}+4 \mathrm{H}_{2} \mathrm{O}\\ \quad \quad \quad \quad \quad \quad \quad \text{Meta phosphoric acid}\)

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

(i) Fluorine is most electronegative atom.
(ii) It has only one unpaired electron.

(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) Its small size
(ii) Its high electronegativity
(iii) Its high ionisation energy
(iv) Non-availability of d-orbital in the valence shell.
(v) Rather inert
(vi) High bond energy

(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.

(i) Helium is used to provide inert atmosphere in electric-arc welding of metals.
(ii) Helium has lowest boiling point hence used in cryogenics.
(iii) It is much less denser than air and hence used for filling air balloons.

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

Chlorine reacts with cold dilute alkali to give chloride and hypochlorite, while with hot concentrated alkali chlorides and chlorates are formed.
\(\mathrm{Cl}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{HCl}+\underset{\text { Hypochlorous acid }}{\mathrm{HOCl}} \)
\(\mathrm{HCl}+\mathrm{NaOH} \rightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O} \)
\(\mathrm{HOCl}+\mathrm{NaOH} \rightarrow \mathrm{NaOCl}+\mathrm{H}_{2} \mathrm{O} \)
                   (Sodium hypo chlorite)
Overall Reaction
3Cl₂ + 6NaOH \(\rightarrow\) NaClO₃ + 5NaCl + 3H₂O
                             (Sodium Chlorate)