Which of the following is only a redox reaction but not a disproportionation reaction?

Which of the following is only a redox reaction but not a disproportionation reaction?
  1. $4 \mathrm{H}_3 \mathrm{PO}_3 ightarrow 3 \mathrm{H}_3 \mathrm{PO}_4+\mathrm{PH}_3$
  2. $2 \mathrm{H}_2 \mathrm{O}_2 ightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2$
  3. $\mathrm{P}_4+3 \mathrm{NaOH}+3 \mathrm{H}_2 \mathrm{O} ightarrow 3 \mathrm{NaH}_2 \mathrm{PO}_2+\mathrm{PH}_3$
  4. $\mathrm{P}_4+8 \mathrm{SOCl}_2 ightarrow 4 \mathrm{PCl}_3+2 \mathrm{~S}_2 \mathrm{Cl}_2+4 \mathrm{SO}_2$

Solution

The reaction $\mathrm{P}_4+8 \mathrm{SOCl}_2 ightarrow 4 \mathrm{PCl}_3+2 \mathrm{~S}_2 \mathrm{Cl}_2+4 \mathrm{SO}_2$ involves change of oxidation state of $\mathrm{P}$ from 0 to +3 and that of $S$ from +4 to +2 . Thus, it is a redox reaction but not a disproportionation reaction.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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