Question

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

• A. \( 4H_3PO_3 \rightarrow 3H_3PO_4 + PH_3 \)
• B. \( 2H_2O_2 \rightarrow 2H_2O + O_2 \)
• C. \( P_4 + 3NaOH + 3H_2O \rightarrow 3NaH_2PO_2 + PH_3 \)
• D. \( P_4 + 8SOCl_2 \rightarrow 4PCl_3 + 2S_2Cl_2 + 4SO_2 \)

Hint:

In a disproportionation reaction, the same element is oxidized and reduced simultaneously. If different elements undergo oxidation and reduction, it is a regular redox reaction.

Answer 1

The Correct Option is D

Step 1: Define Disproportionation and Redox Reactions
A disproportionation reaction occurs when a single element is simultaneously oxidized and reduced. A standard redox reaction, conversely, involves the oxidation and reduction of distinct elements. 
Step 2: Analyze Oxidation States 
Examine the oxidation states of phosphorus (P) and sulfur (S) in the reaction: \[ P_4 + 8SOCl_2 \rightarrow 4PCl_3 + 2S_2Cl_2 + 4SO_2 \] In elemental phosphorus (\( P_4 \)), P has an oxidation state of \( 0 \). 
In phosphorus trichloride (\( PCl_3 \)), P has an oxidation state of \( +3 \). 
In sulfur oxychloride (\( SOCl_2 \)), S has an oxidation state of \( +4 \). 
In disulfur dichloride (\( S_2Cl_2 \)), S has an oxidation state of \( +2 \). 
In sulfur dioxide (\( SO_2 \)), S has an oxidation state of \( +4 \). 
Step 3: Determine Reaction Type 
Phosphorus (\( P \)) is oxidized from \( 0 \) to \( +3 \). 
Sulfur (\( S \)) is reduced from \( +4 \) to \( +2 \). 
As phosphorus only undergoes oxidation and sulfur only undergoes reduction, this is a simple redox reaction, not a disproportionation reaction. 
Step 4: Evaluate Other Options 
Option (A) describes a disproportionation reaction because phosphorus is both oxidized and reduced. 
Option (B) involves the disproportionation of oxygen, changing from \( -1 \) to \( -2 \) and \( 0 \). 
Option (C) also demonstrates the disproportionation of phosphorus.