Question:
Which of the following reactions is not a disproportionation reaction?
Which of the following reactions is not a disproportionation reaction?
Show Hint
In disproportionation reactions, the same element must undergo both oxidation and reduction simultaneously.
Updated On: Jun 24, 2026
- \(\mathrm{CaCO_3 \longrightarrow CaO+CO_2}\)
- \(\mathrm{P_4+3NaOH+3H_2O \longrightarrow 3NaH_2PO_2+PH_3}\)
- \(\mathrm{2H_2O_2 \longrightarrow 2H_2O+O_2}\)
- \(\mathrm{2Cu^+ \longrightarrow Cu^{2+}+Cu}\)
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The Correct Option is A
Solution and Explanation
Step 1: Understand disproportionation reaction.
A disproportionation reaction is a redox reaction in which the same element is simultaneously oxidized and reduced.
That means the same element must show an increase as well as a decrease in oxidation number in the same reaction.
Step 2: Check option (1).
For \[ \mathrm{CaCO_3 \longrightarrow CaO+CO_2} \] Oxidation state of carbon in \(\mathrm{CaCO_3}\) is \[ +4 \] Oxidation state of carbon in \(\mathrm{CO_2}\) is also \[ +4 \] There is no oxidation or reduction of the same element.
So, this is not a disproportionation reaction.
Step 3: Check other options briefly.
In option (2), phosphorus undergoes both oxidation and reduction.
In option (3), oxygen in \(\mathrm{H_2O_2}\) changes from \(-1\) to \(-2\) in water and \(0\) in oxygen.
In option (4), copper changes from \(+1\) to \(+2\) and \(0\).
Hence, options (2), (3), and (4) are disproportionation reactions.
Step 4: Final conclusion.
Therefore, the reaction which is not a disproportionation reaction is \[ \boxed{\mathrm{CaCO_3 \longrightarrow CaO+CO_2}} \]
A disproportionation reaction is a redox reaction in which the same element is simultaneously oxidized and reduced.
That means the same element must show an increase as well as a decrease in oxidation number in the same reaction.
Step 2: Check option (1).
For \[ \mathrm{CaCO_3 \longrightarrow CaO+CO_2} \] Oxidation state of carbon in \(\mathrm{CaCO_3}\) is \[ +4 \] Oxidation state of carbon in \(\mathrm{CO_2}\) is also \[ +4 \] There is no oxidation or reduction of the same element.
So, this is not a disproportionation reaction.
Step 3: Check other options briefly.
In option (2), phosphorus undergoes both oxidation and reduction.
In option (3), oxygen in \(\mathrm{H_2O_2}\) changes from \(-1\) to \(-2\) in water and \(0\) in oxygen.
In option (4), copper changes from \(+1\) to \(+2\) and \(0\).
Hence, options (2), (3), and (4) are disproportionation reactions.
Step 4: Final conclusion.
Therefore, the reaction which is not a disproportionation reaction is \[ \boxed{\mathrm{CaCO_3 \longrightarrow CaO+CO_2}} \]
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