Given below are two statements: Statement (I): Oxidising power of halogens decreases in the order F_{2} > Cl_{2} > Br_{2} > I_{2} , which is the basis of “Layer test”. Statement (II): “Layer test” to identify Br_{2} and I_{2} in aqueous solution involves the oxidation of bromide or iodide into Br_{2} or I_{2} respectively with Cl_{2} , which is a type of displacement redox reaction. In the light of the above statements, choose the correct answer from the options given below:

Both Statement I and Statement II are true

Both Statement I and Statement II are false

Statement I is true but Statement II is false

Statement I is false but Statement II is true

JEE Main · Chemistry · Chapter 7

Redox Reactions JEE Main PYQs (2020–2026)

60 questions from Redox Reactions have appeared in JEE Main between 2020 and 2026, including 48 in the last five papers (2022–2026). The most-asked topic is Oxidation Number & Calculation Rules (17 questions). Practise them all with instant answers and step-by-step solutions.

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Solved Redox Reactions PYQs

3 recent questions with answers. The full set of 60 is free to practise.

JEE Main 2026HardRedox Titrations & Indicators
Q1
500 mL of $0.2 M M n O_{4}^{-}$ 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 $____$ 。
Numerical answer type
Show answer & solution
Correct answer: 1
$3 e^{-} + M n O_{4}^{-} + 2 H_{2} O \to M n O_{2} + 4 O H^{Θ} 2 I^{⊖} \to I_{2} + 2 e^{-} I_{2} + 2 S_{2} O_{3}^{- 2} \to 2 I^{⊖} + S_{4} O_{6}^{- 2}$

gm equivalent of $M n O_{4}^{-}$

$= 0.2 \times \frac{500}{1000} \times 3 = 0.3 (Limiting reagent)$

gm equivalent of KI

$= 1.5 \times \frac{500}{1000} \times 1 = 0.75$

gm equivalent of $M n O_{4}^{-}$

= gm equivalent of hypo

$0.3 = x \times \frac{300}{1000} \times 1 x = 1$
JEE Main 2026MediumBalancing Redox Reactions (Ion-Electron & Oxidation State)
Q2
X and Y are the number of electrons involved, respectively during the oxidation of $I^{-}$ to $I_{2}$ and $S^{2 -}$ to S by acidified $K_{2} C r_{2} O_{7}$ . The value of $X + Y$ is $____$ .
Numerical answer type
Show answer & solution
Correct answer: 12
$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 I^{-} \to 2 C r^{3 +} + 3 I_{2} + 7 H_{2} O$

In this reaction, $6 I^{-}$ ions get oxidised to $3 I_{2}$ .

Each $I^{-}$ loses $1$ electron during oxidation, so total electrons lost (in moles) $= X = 6$ .

$C r_{2} O_{7}^{2 -} + 3 S^{2 -} + 14 H^{+} \to + S + 2 C r^{3 +} + 7 H_{2} O$

Here, $3 S^{2 -}$ ions get oxidised to $3 S$ .

Each $S^{2 -}$ loses $2$ electrons to become $S$ , so total electrons lost (in moles) $= Y = 3 \times 2 = 6$ .

Therefore, $x + y = 6 + 6 = 12$ .
JEE Main 2026EasyElectrochemical Series & Standard Electrode Potential
Q3
Given below are two statements:

Statement (I): Oxidising power of halogens decreases in the order $F_{2} > C l_{2} > B r_{2} > I_{2}$ , which is the basis of “Layer test”.

Statement (II): “Layer test” to identify $B r_{2}$ and $I_{2}$ in aqueous solution involves the oxidation of bromide or iodide into $B r_{2}$ or $I_{2}$ respectively with $C l_{2}$ , which is a type of displacement redox reaction.

In the light of the above statements, choose the correct answer from the options given below:
- ABoth Statement I and Statement II are true
- BBoth Statement I and Statement II are false
- CStatement I is true but Statement II is false
- DStatement I is false but Statement II is true
Show answer & solution
Correct answer: (A)
The oxidising power of halogens decreases in the order $F_{2} > C l_{2} > B r_{2} > I_{2}$ . This means that fluorine is the strongest oxidising agent and iodine is the weakest. Therefore, $C l_{2}$ can easily oxidise bromide and iodide ions to form $B r_{2}$ and $I_{2}$ respectively. This principle is used in the “Layer test”.

In this test, chlorine gas is passed through an aqueous solution containing bromide or iodide ions. A redox (oxidation-reduction) reaction takes place, where chlorine oxidises bromide or iodide ions. The chemical equations are as follows:

$N a B r + Cl_{2} \to B r_{2} + N a Cl$

$N a I + Cl_{2} \to I_{2} + N a Cl$

So, $C l_{2}$ displaces $B r_{2}$ and $I_{2}$ from their compounds since chlorine has higher oxidising power. This confirms that both statements (I) and (II) are true, and statement (II) correctly explains statement (I).