JEE Main · 2022 · Shift-IImediumRDX-037

Given below are two statements: Statement I: S8 solid undergoes disproportionation reaction under alkaline conditions…

Redox Reactions · Class 11 · JEE Main Previous Year Question

Question

Given below are two statements:

Statement I: S8\mathrm{S_8} solid undergoes disproportionation reaction under alkaline conditions to form S2−\mathrm{S^{2-}} and S2O32−\mathrm{S_2O_3^{2-}}. Statement II: ClO4−\mathrm{ClO_4^{-}} can undergo disproportionation reaction under acidic condition.

In the light of the above statements, choose the most appropriate answer from the options given below:

Options
  1. a

    Statement I is correct but Statement II is incorrect.

    ✓
  2. b

    Statement I is incorrect but Statement II is correct

  3. c

    Both Statement I and Statement II are incorrect

  4. d

    Both Statement I and Statement II are correct

Correct Answera

Statement I is correct but Statement II is incorrect.

Detailed Solution

Step 1 — Evaluate Statement I:

S8\mathrm{S_8} in alkaline medium: S8+12OH−→4S2−+2S2O32−+6H2O\mathrm{S_8 + 12OH^- \rightarrow 4S^{2-} + 2S_2O_3^{2-} + 6H_2O}

  • S in S8\mathrm{S_8}: OS = 00
  • S in S2−\mathrm{S^{2-}}: OS = −2-2 (reduced)
  • S in S2O32−\mathrm{S_2O_3^{2-}}: average OS = +2+2 (oxidised)

Same element (S) simultaneously oxidised and reduced → Disproportionation ✓ Statement I is CORRECT ✓

Step 2 — Evaluate Statement II:

ClO4−\mathrm{ClO_4^-} (perchlorate): Cl is in its highest oxidation state (+7). It cannot be further oxidised → cannot undergo disproportionation.

ClO4−\mathrm{ClO_4^-} can only act as an oxidising agent (be reduced), not disproportionate. Statement II is INCORRECT ✗

Answer: Option (1) — Statement I correct, Statement II incorrect

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