Which of the following is not a disproportionation reaction? o I. NH NO N O 2H O II.P 3NaOH 3H O P H — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

# Solution A **disproportionation reaction** occurs when a single element in one oxidation state is simultaneously oxidized AND reduced to form two different oxidation states. Let me analyze each reaction: **I. $2NH_3 \rightarrow N_2 + 3H_2O$** - N in $NH_3$: oxidation state = -3 - N in $N_2$: oxidation state = 0 - Some N is oxidized (-3 → 0) while being reduced simultaneously - **This IS disproportionation** ✓ **II. $P_4 + 3NaOH + 3H_2O \rightarrow PH_3 + 3NaH_2PO_2$** - P in $P_4$: oxidation state = 0 - P in $PH_3$: oxidation state = -3 (reduced) - P in $NaH_2PO_2$: oxidation state = +1 (oxidized) - Same element in one oxidation state (0) forms two different products - **This IS disproportionation** ✓ **III. $PCl_5 \rightarrow PCl_3 + Cl_2$** - P: oxidation state = +5 in both $PCl_5$ and $PCl_3$ (NO CHANGE in P) - Cl in $PCl_5$: oxidation state = -1 - Cl in $PCl_3$: oxidation state = -1 (NO CHANGE) - Cl in $Cl_2$: oxidation state = 0 (but different element source) - **This is NOT disproportionation** — it's a decomposition reaction **IV. $IO_3^- + 5I^- + 6H^+ \rightarrow 3I_2 + 3H_2O$** - I in $IO_3^-$: +5 (reduced to 0 in $I_2$) - I in $I^-$: -1