Redox Reactions — JEE Main PYQs (Chemistry)

ChemistryJEE Main 23 Jan 2026, Shift 2·Q23·Numerical·Easy–moderate

Redox titration dichromate mohr salt

200 cc of $x\times10^{-3}$ M potassium dichromate is required to oxidise 750 cc of 0.6 M Mohr's salt solution in acidic medium.

Here $x =$

ChemistryJEE Main 24 Jan 2026, Shift 1·Q25·Numerical·Easy–moderate

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Electrons transferred dichromate oxidation

X and Y are the number of electrons involved, respectively during the oxidation of $\ce{I^-}$ to $\ce{I2}$ and $\ce{S^{2-}}$ to S by acidified $\ce{K2Cr2O7}$ . The value of X + Y is .

(Consider the electrons transferred per mole of $\ce{K2Cr2O7}$ reduced in each reaction)

We corrected a printing error in the original paper

Assumption “(Consider the electrons transferred per mole of $\ce{K2Cr2O7}$ reduced in each reaction)” added; the source leaves it unstated (per $\ce{I2}$ /S formed it would be 2 + 2 = 4).

ChemistryJEE Main 28 Jan 2026, Shift 1·Q21·Numerical·Moderate

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Iodometric titration equivalents

500 mL of 1.2 M KI solution is mixed with 500 mL of 0.2 M

\ce{KMnO4}

solution in basic medium. The liberated iodine was titrated with standard 0.1 M

\ce{Na2S2O3}

solution in the presence of starch indicator till the blue color disappeared. The volume (in L) of

\ce{Na2S2O3}

consumed is . (Nearest integer)

ChemistryJEE Main 28 Jan 2026, Shift 1·Q22·Numerical·Moderate

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Balancing redox reactions

Consider the following redox reaction taking place in acidic medium

$\ce{BH4^-(aq) + ClO3^-(aq) -> H2BO3^-(aq) + Cl^-(aq)}$

If the Nernst equation for the above balanced reaction is $E_\mathrm{cell} = E^\circ_\mathrm{cell} - \frac{RT}{nF}\ln Q,$ Then the value of $n$ is . (Nearest integer)

ChemistryJEE Main 2 Apr 2026, Shift 1·Q10·MCQ·Easy–moderate

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Halogen displacement and layer test

Given below are two statements :

Statement (I) : Oxidising power of halogens decreases in the order $\ce{F2}$ $>$ $\ce{Cl2}$ $>$ $\ce{Br2}$ $>$ $\ce{I2}$ , which is the basis of “Layer test”.

Statement (II) : “Layer test” to identify $\ce{Br2}$ and $\ce{I2}$ in aqueous solution involves the oxidation of bromide or iodide into $\ce{Br2}$ or $\ce{I2}$ respectively with $\ce{Cl2}$ , which is a type of displacement redox reaction.

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

(1)Both Statement I and Statement II are true
(2)Both Statement I and Statement II are false
(3)Statement I is true but Statement II is false
(4)Statement I is false but Statement II is true

ChemistryJEE Main 4 Apr 2026, Shift 1·Q6·MCQ·Moderate

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Redox titration equivalents

In order to oxidise a mixture of 1 mole each of

\ce{FeC2O4}

,

\ce{Fe2(C2O4)3}

,

\ce{FeSO4}

and

\ce{Fe2(SO4)3}

in acidic medium, the number of moles of

\ce{KMnO4}

required is :

(1)3
(2)2
(3)5
(4)7

ChemistryJEE Main 6 Apr 2026, Shift 2·Q23·Numerical·Moderate

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Iodometric redox titration

500 mL of 0.2 M

\ce{MnO4-}

solution in basic medium when mixed with 500 mL of 1.5 M KI solution, oxidises iodide ions to liberate molecular iodine. This liberated iodine is then titrated with a standard

x

M thiosulphate solution in presence of starch till the end point. If 300 mL of thiosulphate was consumed, then the value of

x

is .