Which of the following chemical reactions depict the oxidizing beahviour of $\mathrm{H}_{2} \mathrm{SO}_{4}$ ?

Which of the following chemical reactions depict the oxidizing beahviour of $\mathrm{H}_{2} \mathrm{SO}_{4}$ ?
  1. $\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{NaHSO}_{4}+\mathrm{HCl}$
  2. $2 \mathrm{PCl}_{5}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow 2 \mathrm{POCl}_{3}+2 \mathrm{HCl}+\mathrm{SO}_{2} \mathrm{Cl}_{2}$
  3. $2 \mathrm{HI}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{I}_{2}+\mathrm{SO}_{2}+2 \mathrm{H}_{2} \mathrm{O}$
  4. $\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{CaSO}_{4}+2 \mathrm{H}_{2} \mathrm{O}$

Solution

$2 \mathrm{HI}^{-1}+\mathrm{H}_{2}^{+6} \mathrm{SO}_{4} \longrightarrow \mathrm{I}_{2}^{0}+\stackrel{+4}{\mathrm{~S}} \mathrm{O}_{2}+2 \mathrm{H}_{2} \mathrm{O}$
In thisreaction oxidation number of $S$ is decreasing from $+6$ to $+4$ hence undergoing reduction and for HI oxidation Number of I is increasing from $-1$ to 0 hence underegoing oxidation therefore $\mathrm{H}_{2} \mathrm{SO}_{4}$ is acting as oxidising agent.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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