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NEET UG 2021 · Chemistry · Question 96

NEET 2021 Chemistry, question 96

Question 96 of the NEET 2021 paper (code O1) is a Chemistry question from Thermodynamics. Its idea, Entropy of Isothermal Gas Expansion, was asked only this once in NEET 2017–2026. The NTA final answer key gives option 1.

Updated 2026-10-08

Q96 · Chemistry

For irreversible expansion of an ideal gas under isothermal condition, the correct option is :

  1. 1ΔU=0\Delta U = 0, ΔStotal≠0\Delta S_{total} \neq 0Official answer
  2. 2ΔU≠0\Delta U \neq 0, ΔStotal=0\Delta S_{total} = 0
  3. 3ΔU=0\Delta U = 0, ΔStotal=0\Delta S_{total} = 0
  4. 4ΔU≠0\Delta U \neq 0, ΔStotal≠0\Delta S_{total} \neq 0

Official answer: option 1 · NTA final answer key

Same idea

The only question on Entropy of Isothermal Gas Expansion

No other NEET paper from 2017–2026 tested this exact idea.

Entropy of Isothermal Gas Expansion: every question and how it was framed

The chapter

Thermodynamics in ten years of NEET

32 questions from 2017–2026, asked in 10 of 10 papers, about 3.1 a paper. Gibbs Free Energy alone had 7.

Chapter analysisStudy this chapterPractise this chapter

Thermodynamics: questions per paper

0364’174’183’193’202’212’222’234’243’255’26