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MHT CET202519 Apr 2025Evening ShiftChemistryThermodynamics (C)Actual

Which of the following reactions exhibits decrease in entropy?

Options

  1. A2 H ₂ O _ 2(l) 2 H ₂ O _ (l) + O _ 2( ~g )
  2. BH _ 2( ~g ) 2 H _ ( g )
  3. CCaCO _ 3( ~s ) CaO _ ( s ) + CO _ 2( ~g )
  4. D2 H _ 2( ~g ) + O _ 2( ~g ) 2 H ₂ O _ ( l )

Correct answer

D. 2 H _ 2( ~g ) + O _ 2( ~g ) 2 H ₂ O _ ( l )

Step-by-step solution

Decrease in Entropy Analysis Entropy decreases when the number of gaseous moles reduces or when matter transitions to a more ordered phase. For reaction D: 2 H _ 2( g ) + O _ 2( g ) 2 H ₂ O _ ( l ) , reactants total 3 moles of gas, while products yield 2 moles of liquid. The reduction from 3 gaseous moles to 0 coupled with the gas-to-liquid phase transition results in decreased entropy. Thus, the correct choice is D .

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