In the summer season, nitrogen dioxide and methane react with chlorine monoxide and chlorine free radicals forming chlorine sinks, preventing much ozone depletion, whereas in winters, special type of clouds, called the polar stratospheric clouds are formed over Antarctica.
These polar stratospheric clouds provide the surface on which chlorine nitrate gets hydrolysed to form hypochlorous acid.It also reacts with hydrogen chloride to give molecular chlorine.
\({ CIO }^{ . }\left( g \right) +N{ O }_{ 2 }\left( g \right) \longrightarrow { CIONO }_{ 2 }\left( g \right) \)
\({ Cl }^{ . }\left( g \right) +{ CH }_{ 4 }\left( g \right) \longrightarrow { CH }_{ 3 }\left( g \right) +HCI\left( g \right) \)
\( { CIONO }_{ 2 }\left( g \right) +{ H }_{ 2 }O\left( g \right) \longrightarrow HOCI\left( g \right) +HN{ O }_{ 3 }\left( g \right) \)
\( { CIONO }_{ 2 }\left( g \right) +HCI\left( g \right) \longrightarrow { CI }_{ 2 }\left( g \right) +HN{ O }_{ 3 }\left( g \right) \)
When sunlight returns to the Antarctica in the spring, the Sun's warmth breaks up the clouds and HOCI and CI₂ are photolysed by sunlight.
\( \mathrm{HOCl}(g) \stackrel{h \mathrm{v}}{\longrightarrow} \dot{\mathrm{O}} \cdot \mathrm{H}(g)+\dot{\mathrm{Cl}}(\mathrm{g}) \)
\(\mathrm{Cl}_{2}(g) \stackrel{h \mathrm{v}}{\longrightarrow} 2 \overline{\mathrm{C}} \mathrm{l}(\mathrm{g}) \)
The chlorine radicals thus formed, initiate the chain for ozone depletion.

Peroxide effect is not observed in addition of HCl and HI. This is due to fact that the H__Cl bond being stronger (430.5 kJ mol^-1) than H__Br bond (363.7 kJ mol^-1) is not cleaved by the free radical whreas the H___I bond is weaker (296.8 kJ mol^-1) and iodine free radicals combine to form iodine molecules instead of adding to the double bond.

I and II, III and IV and, VI and VII represent position isomerism.

Due to strong inert pair effect, +1 oxidation state of Tl is more stable than +3. since, compounds in lower oxidation state are ionic but covalent in higher oxidation state, therefore TlCl₃ is less stable and covalent in nature but TlCl is more stable and is ionic in nature.

Hydrogen resembles alkali metals, i.e. Li, Na, K, Rb, Cs and Fr of group I of the periodic table in the following respects.
(i) Like alkali metals, hydrogen also contain one electron in its outermost (valence) shell and exhibit +1 oxidation state.
(ii) Like alkali metals, hydrogen also loses its only electron to form hydrogen ion, i.e.H⁺ (proton).
(iii) Like alkali metals, hydrogen combines with electronegative elements (non-metals) such as oxygen, halogens and sulphides respectively.
(iv) Like alkali metals, hydrogen also acts as a strong reducing agent.

Formal charge on an atom in a Lewis structure
= [total number of valence electrons in free atom]
- [total number of non-bonding (lone pairs) electrons]
- \(\frac { 1 }{ 2 } \)[total number of bonding or shared electron]
Formal charge on H = 1 - 0 x 2 = 0
Formal charge on N = 5 - 0 x 8 = 1
Formal charge on O (1) = 6 - 4 - x 4 = 0
Formal charge on O (2) = 6 - 4 - x 4 = 0
Formal charge on O (3) = 6 - 6 - x 2 = -1


On solving we get, formal charges on O(1), N and O(2) as 0, +1 and -1 respectively. 
Similarly, on solving we get formal charge on H(1), H(2), O(2), O(3), O(4) ans S, as 0, 0, 0, -1 , 0, -1 and +2 respectively.

Temperature corresponding to 60 mm \(\simeq \) 313 K.