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Friday, 9 October

NEET UG 2018 · Chemistry · Question 81

NEET 2018 Chemistry, question 81

Question 81 of the NEET 2018 paper (code AA) is a Chemistry question from Electrochemistry. Its idea, Spontaneity of Disproportionation Reactions, was asked only this once in NEET 2017–2026. The CBSE official answer key gives option 4.

Updated 2026-10-08

Q81 · Chemistry

Consider the change in oxidation state of Bromine corresponding to different emf values as shown in the diagram below :

BrO4−→1.82 VBrO3−→1.5 VHBrO→1.595 VBr2→1.0652 VBr−\mathrm{BrO_4^-} \xrightarrow{1.82\ \mathrm{V}} \mathrm{BrO_3^-} \xrightarrow{1.5\ \mathrm{V}} \mathrm{HBrO} \xrightarrow{1.595\ \mathrm{V}} \mathrm{Br_2} \xrightarrow{1.0652\ \mathrm{V}} \mathrm{Br^-}

Then the species undergoing disproportionation is

The figure, described in words

Emf ladder (Latimer-type) diagram in the stem: BrO4- -> BrO3- (1.82 V) -> HBrO (1.5 V) -> Br2 (1.595 V) -> Br- (1.0652 V), with potentials labelled on the arrows.

  1. 1Br2\mathrm{Br_2}
  2. 2BrO4−\mathrm{BrO_4^-}
  3. 3BrO3−\mathrm{BrO_3^-}
  4. 4HBrOOfficial answer

Official answer: option 4 · CBSE official answer key

Same idea

The only question on Spontaneity of Disproportionation Reactions

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

Spontaneity of Disproportionation Reactions: every question and how it was framed

The chapter

Electrochemistry in ten years of NEET

17 questions from 2017–2026, asked in 10 of 10 papers, about 1.6 a paper. Nernst Equation alone had 9.

Chapter analysisStudy this chapterPractise this chapter

Electrochemistry: questions per paper

0241’171’182’192’202’212’222’232’241’252’26