Chemistry Q61 – JEE-MAIN 2026

Home Chemistry Redox ReactionsQuestion #552

Which of the following sets includes all the species that will change the orange colour of

K_{2} C r_{2} O_{7}

in acidic medium ?

Clue 1 of 3: Identify the role of dichromate

Potassium dichromate ( $K_{2} C r_{2} O_{7}$ ) in acidic medium acts as a strong oxidizing agent, meaning it will get reduced.

🧠 Full Solution Path

Step 1: Understand the role of Dichromate in Acidic Medium✦ Active

In acidic medium, the dichromate ion ( $C r_{2} O_{7}^{2 -}$ ), which is orange, acts as a strong oxidizing agent. It gets reduced to the green chromium(III) ion ( $C r^{3 +}$ ). The half-reaction is:

C r_{2} O_{7}^{2 -} (o r a n g e) + 14 H^{+} + 6 e^{-} \to 2 C r^{3 +} (g r e e n) + 7 H_{2} O

Therefore, any species that can be oxidized by $C r_{2} O_{7}^{2 -}$ (i.e., acts as a reducing agent) will cause this color change.

Step 2: Evaluate each option for reducing agents○ Expand

We need to identify the set where all species can be oxidized (are reducing agents):

1. $F e^{2 +}$ can be oxidized to $F e^{3 +}$ . $S n^{2 +}$ can be oxidized to $S n^{4 +}$ . $I^{-}$ can be oxidized to $I_{2}$ . $S^{2 -}$ can be oxidized to $S$ or $S O_{2}$ or $S O_{4}^{2 -}$ . All are reducing agents.

2. $F e^{3 +}$ is already in a higher oxidation state and cannot be oxidized further by $C r_{2} O_{7}^{2 -}$ . It is not a reducing agent in this context.

3. $S n^{4 +}$ is already in its highest oxidation state and cannot be oxidized further by $C r_{2} O_{7}^{2 -}$ . It is not a reducing agent.

4. $F e^{3 +}$ , $S O_{4}^{2 -}$ (sulfur in +6 oxidation state), and $S n^{4 +}$ cannot be oxidized further by $C r_{2} O_{7}^{2 -}$ . They are not reducing agents.

💡 Teacher's Secret Hint

Remember to check the maximum possible oxidation state for each element to determine if it can act as a reducing agent.

Step 3: Conclusion○ Expand

Only the set in option 1 contains all species ( $F e^{2 +}$ , $S n^{2 +}$ , $I^{-}$ , $S^{2 -}$ ) that are reducing agents and will react with $K_{2} C r_{2} O_{7}$ in acidic medium, causing the orange color to change to green.

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Chemistry Question 61 – JEE-MAIN 2026

Clue 1 of 3: Identify the role of dichromate

🧠 Full Solution Path