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  3. Chemistry
  4. Give reasons in two or three sentences only for (i) Bond dissociation energy of F2 is less than that of Cl2. (ii) Sulphur dioxide is a more powerful reducing agent in the alkaline medium than in acidic medium.

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Q. Give reasons in two or three sentences only for
(i) Bond dissociation energy of $F_2$ is less than that of $Cl_2.$
(ii) Sulphur dioxide is a more powerful reducing agent in the alkaline medium than in acidic medium.

IIT JEEIIT JEE 1992The p-Block Elements - Part2

Solution:

(i) Due to small size and high electron density of fluorine atom, there exist a significant repulsions between fluorine atoms in $F_2,$ they have greater tendency to get apart. Hence, bond energy of $F_2$ is less than that of $Cl_2.$
This is against to bond-length bond-energy relationship,.
(ii) Sulphur dioxide is a more powerful reducing agent in alkaline medium because nascent hydrogen is produced in the presence of moisture
i.e. $SO_2 + 2H_2O \longrightarrow H_2SO_4 + 2H$
And alkaline solution neutralises the acid i.e. $H_2SO_4$ and shift the equilibrium in the forward direction producing more nascent hydrogen. But in acidic medium the equilibrium will suppressed resulting in a lesser amount of nascent hydrogen.