JEE Advanced Chemistry 2025 Analysis - Top Skipped, Wrongly Attempted and Correctly Solved Questions

JEE Advanced 2025 Chemistry Analysis - Paper 1 and Paper 2 Question-Wise Candidate’s Performance

Most Skipped Chemistry Questions (High Non-Attempt %)

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Paper 2

JEE Advanced Chemistry Paper 2 Question 7

Solution:

Starting naphthalene $\rightarrow \mathrm{KMnO}_4 / \mathrm{H}^{+}, \Delta \rightarrow$ phthalic acid $\rightarrow \mathrm{NH}_3, \Delta\left(-2 \mathrm{H}_2 \mathrm{O}\right) \rightarrow \mathrm{X}=$ phthalimide.

Phthalimide $(\mathrm{X}) \rightarrow \mathrm{KOH} / \mathrm{EtOH} \rightarrow \mathrm{N}$-alkylation with $\mathrm{R}-\mathrm{Br} \rightarrow \mathrm{Y}=\mathrm{N}$-alkylphthalimide (Gabriel synthesis).

NaOH hydrolysis of $Y \rightarrow$ phthalate (aromatic) $+Z=\mathrm{RNH}_2$ (primary amine).

So,

(A) X and Y both contain oxygen $\rightarrow$ True.

(B) Y is not a primary amine $\rightarrow$ no carbylamine test $\rightarrow$ False.

(C) Z is a primary amine, gives Hinsberg reaction $\rightarrow$ True.

(D) Z is aliphatic (Gabriel with $\mathrm{R}-\mathrm{Br}=$ alkyl); aryl halides don't undergo $\mathrm{SN} 2 \rightarrow$ False.

Hence, the correct answers are option 1,3.

Why most students skip this question?

1. Multi-step Conversion Chain

The reaction required linking oxidation → phthalimide formation → Gabriel synthesis → hydrolysis. Many candidates are comfortable with one or two-step conversions, but this was a 4-step reasoning chain, which discouraged attempts under time pressure.

2. Less Familiar Intermediate

The key intermediate here is phthalimide, which is not a very common NCERT-level compound in everyday practice questions. Since many students hadn’t memorized that naphthalene oxidation → phthalic acid → phthalimide, they struggled to identify “X” confidently.

3. Conceptual Traps in Options

• Option (B) tempted students with the carbylamine test, but the intermediate Y is not a primary amine.
  

• Option (D) suggested Z is an aromatic amine, but Gabriel synthesis doesn’t yield aryl amines.
  Such traps raised doubt even if students followed part of the mechanism.
  

4. Time Management Pressure

This problem was placed among organic reaction sequence questions, which are usually time-consuming. Many aspirants skipped it to avoid losing time on an unfamiliar, lengthy pathway, preferring quicker physical or inorganic chemistry questions.

Most Wrongly Attempted Chemistry Questions (High Wrong Response %)

Paper 1

Paper 2

JEE Advanced Chemistry Paper 2 Question 14

Question 14: An electrochemical cell is fueled by the combustion of butane at 1 bar and 298 K . Its cell potential is $\frac{\boldsymbol{X}}{\boldsymbol{F}} \times 10^3$ volts, where $F$ is the Faraday constant. The value of $\boldsymbol{X}$ is $\qquad$ .

Use: Standard Gibbs energies of formation at 298 K are: $\Delta_f G_{\mathrm{CO}_2}^o=-394 \mathrm{~kJ} \mathrm{~mol}^{-1} ; \Delta_f G_{\text {water }}^o= -237 \mathrm{~kJ} \mathrm{~mol}^{-1} ; \Delta_f G_{\text {butane }}^o=-18 \mathrm{~kJ} \mathrm{~mol}^{-1}$

Solution:

Given

Combustion fuel cell at $298 \mathrm{~K}, 1 \mathrm{bar}$.

$\mathrm{C}_4 \mathrm{H}_{10}+\frac{13}{2} \mathrm{O}_2 \rightarrow 4 \mathrm{CO}_2+5 \mathrm{H}_2 \mathrm{O}(\mathrm{l})$

$\Delta_f G^{\circ}\left(\mathrm{CO}_2\right)=-394 \mathrm{~kJ} \mathrm{~mol}^{-1}, \quad \Delta_f G^{\circ}\left(\mathrm{H}_2 \mathrm{O}(\mathrm{l})\right)=-237 \mathrm{~kJ} \mathrm{~mol}^{-1}, \quad \Delta_f G^{\circ}\left(\mathrm{C}_4 \mathrm{H}_{10}\right)=-18 \mathrm{~kJ} \mathrm{~mol}^{-1}$

1) Reaction Gibbs energy

$\Delta G_{\mathrm{rxn}}^{\circ} $ =$[4(-394)+5(-237)]-(-18)+\frac{13}{2}(0)$

$=(-1576-1185)-(-18)$

$=-2761+18$

$=-2743 \mathrm{~kJ} \mathrm{~mol}^{-1}$

2) Electrons transferred $n$

Average oxidation state of $C$ in butane: $4 x+10(+1)=0 \Rightarrow x=-2.5$.

In $\mathrm{CO}_2, \mathrm{C}$ is +4 . Change per $\mathrm{C}=+6.5$.

For 4 carbons: $n=4 \times 6.5=26$ electrons.

(Equivalently, for $\mathrm{C}_{\mathrm{a}} \mathrm{H}_{\mathrm{b}} \mathrm{O}_{\mathrm{c}}: n=4 a+b-2 c=4 \cdot 4+10-0=26$.)

3) Cell potential

$E^{\circ}=\frac{-\Delta G_{\mathrm{rxn}}^{\circ}}{n F}=\frac{2743 \mathrm{~kJ} \mathrm{~mol}^{-1}}{26 F}=\frac{105.5}{F} \times 10^3 \mathrm{~V}$

so $X=105.5$.

(For reference, $E^{\circ} \approx 1.09 \mathrm{~V}$ using $F=96485 \mathrm{C} \mathrm{mol}^{-1}$.)

Hence, the correct answer is 105.5

Why many students got it wrong?

1. Complex Multi-Step Approach Involving Thermodynamics & Electrochemistry

• The problem required combining Gibbs energy calculations with electrochemistry concepts in one integrated framework. Many students are comfortable with each part separately, but finding and applying the link between ΔG° of reaction → cell potential can be challenging under exam pressure.
  

2. Mistakes in Reaction Balance or Electron Count

• Students often miscalculate the stoichiometry, especially:

• Balancing the combustion reaction for butane correctly (C₄H₁₀ + 13/2 O₂ → 4 CO₂ + 5 H₂O).
• Counting the exact number of electrons transferred (n = 26). Some mistakenly use 24 or 28 (e.g., assuming each carbon change from –2.5 to +4 was +6 incorrectly or forgetting hydrogen’s involvement), which then distorts the E° calculation.

3. Gibbs Energy ΔG° Even vs. Molar Quantities

• The key step: compute ΔG° for the complete reaction using formation energies. Errors include:
  

• • Forgetting to subtract formation Gibbs energy of butane—which is negative.

  • Using standard enthalpies instead of Gibbs energies (mixing up ΔH° vs. ΔG°).

  • Miscounting product coefficients ( $5 \mathrm{H}_2 \mathrm{O}$ not 4 or 6 )

4. Time Pressure & Cognitive Load

• With multiple calculation steps—reaction balancing → ΔG° → electrons transferred → unit conversions—students under time constraints tend to skip detailed re-checks. Any small slip along the way compounds to an incorrect final value.

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Most Correctly Solved Chemistry Questions (Higher Accuracy)

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Paper 2

Marks of First and Last Ranked Candidates in Each Category

Distribution of Total Marks in Aggregate (all, qualified, and allotted candidates)

For All Candidates

For Qualified Candidates

For Seat Allotted Candidates

JEE Advanced 2025 Chemistry: Most Difficult Questions

Paper 1

The most difficult questions in JEE Advanced chemistry Paper 1 (Q13, Q11, Q10, Q9) turned out to be challenging due to a mix of high wrong response rates and very low full marks percentages. Questions 9 and 11 have, on average, 75.35% wrong attempts. This shows that students found the questions easy, but they fell into the trap. As a result, they ended up making wrong attempts. And Question 13 is the least full-mark (0.48%) question.

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