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2026 Statistics

Key Facts: NSEC Exam

Official Exam Questions

IAPT Syllabus

2 hours

Time Limit

IAPT

₹300

Registration Fee

IAPT 2025-2026

Hard

Difficulty Level

Olympiad Standards

Stage 1

Olympiad Level

IChO Selection Route

State-wise Pass Rate

INChO Selection Clause

NSEC is the first-stage Chemistry Olympiad screening test in India. The 2-hour offline exam consists of 60 questions (48 single-choice and 12 multi-choice) for a total of 216 marks. The entry fee is ₹300. Aligned with Class XI-XII CBSE Chemistry but at a much higher problem-solving level, it focuses heavily on reaction mechanisms, chemical thermodynamics, coordination compounds, and stereochemistry. Qualifying candidates proceed to the INChO.

Sample NSEC Practice Questions

Try these sample questions to test your NSEC exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1For the oxidation-reduction reaction of ferrous oxalate (FeC2O4) with potassium dichromate (K2Cr2O7) in an acidic medium, how many moles of K2Cr2O7 are required to oxidize one mole of FeC2O4 completely?

A.1/2 mole

B.1/3 mole

C.3/6 (or 1/2) mole

D.5/6 mole

Explanation: In an acidic medium, FeC2O4 is oxidized to Fe3+ and CO2. The oxidation state of Fe changes from +2 to +3 (loss of 1 electron), and the oxidation state of carbon changes from +3 to +4 (each oxalate carbon loses 1 electron, total 2 electrons). Thus, one mole of FeC2O4 releases a total of 3 moles of electrons. Potassium dichromate (Cr2O7^2-) is reduced to Cr3+ in an acidic medium, where each chromium atom gains 3 electrons, meaning one mole of Cr2O7^2- accepts 6 moles of electrons. By electron balance, 3 moles of electrons from FeC2O4 require 3/6 = 0.5 (or 1/2) moles of K2Cr2O7.

2An oleum sample is labeled as '109%'. What is the mass percentage of free SO3 in this sample of oleum?

A.9.0%

B.40.0%

C.90.0%

D.9.9%

Explanation: An oleum label of '109%' means that 100 g of oleum requires 9 g of water to react completely with all free SO3 to form H2SO4. The reaction is SO3 + H2O -> H2SO4. From the stoichiometry, 18 g of H2O reacts with 80 g of SO3. Therefore, 9 g of H2O reacts with (80/18) * 9 = 40 g of SO3. Since this SO3 was present in 100 g of the oleum sample, the mass percentage of free SO3 is 40.0%.

3According to the Bohr model, which electronic transition in a He+ ion will have the same wavelength as the transition from n = 4 to n = 2 in a hydrogen atom?

A.n = 4 to n = 2

B.n = 8 to n = 4

C.n = 6 to n = 3

D.n = 2 to n = 1

Explanation: The Rydberg formula for wavelength is 1/lambda = R * Z^2 * (1/n1^2 - 1/n2^2). For hydrogen (Z = 1) from n = 4 to n = 2, the term is (1/2^2 - 1/4^2) = 3/16. For He+ (Z = 2), to get the same wavelength, we need Z^2 * (1/n1^2 - 1/n2^2) = 4 * (1/n1^2 - 1/n2^2) = 3/16. This simplifies to (1/n1^2 - 1/n2^2) = 3/64. Testing n = 8 to n = 4 gives (1/4^2 - 1/8^2) = (1/16 - 1/64) = 3/64. Multiplying this by He+'s Z^2 (4) yields 3/16, which matches the hydrogen transition.

4What is the total number of radial nodes and angular nodes, respectively, in a 4d orbital of a hydrogen-like atom?

A.2 radial nodes, 2 angular nodes

B.1 radial node, 2 angular nodes

C.2 radial nodes, 1 angular node

D.3 radial nodes, 0 angular nodes

Explanation: For any orbital, the number of radial nodes is given by n - l - 1, and the number of angular nodes is equal to the azimuthal quantum number l. For a 4d orbital, the principal quantum number n = 4 and the azimuthal quantum number l = 2. Therefore, the number of radial nodes is 4 - 2 - 1 = 1, and the number of angular nodes is l = 2.

5When a metal surface is illuminated with light of wavelength 300 nm, photoelectric emission occurs. If the work function of the metal is 2.5 eV, what is the maximum kinetic energy of the emitted photoelectrons? (Take hc = 1240 eV-nm)

A.1.63 eV

B.4.13 eV

C.2.50 eV

D.1.13 eV

Explanation: According to Einstein's photoelectric equation, KE_max = E_photon - Phi, where Phi is the work function. The energy of the incident photon is E_photon = hc / lambda = 1240 eV-nm / 300 nm = 4.13 eV. Using the work function of 2.5 eV, the maximum kinetic energy is KE_max = 4.13 eV - 2.50 eV = 1.63 eV.

6Under which conditions does the compressibility factor (Z) of a real gas obeying the van der Waals equation become Z = 1 + (Pb / RT)?

A.At very low pressures

B.At very high pressures

C.At extremely low temperatures

D.At the Boyle temperature

Explanation: The van der Waals equation is (P + a/V^2)(V - b) = RT. At very high pressures, the volume V is small, so the term a/V^2 is negligible compared to the high pressure P. The equation simplifies to P(V - b) = RT, which gives PV - Pb = RT, or PV/RT = 1 + Pb/RT. Since Z = PV/RT, we get Z = 1 + Pb/RT, meaning the gas is less compressible than an ideal gas due to dominant molecular repulsive forces.

7A vessel contains equal masses of methane (CH4) and oxygen (O2) gases. What is the ratio of the partial pressure of methane to that of oxygen in the vessel?

A.1 : 1

B.2 : 1

C.1 : 2

D.4 : 1

Explanation: According to Dalton's Law of Partial Pressures, the partial pressure of a gas in a mixture is proportional to its mole fraction. Let the mass of both CH4 and O2 be w grams. The number of moles of CH4 is w / 16, and the number of moles of O2 is w / 32. The ratio of the moles of CH4 to O2 is (w/16) : (w/32) = 2 : 1. Since the volume and temperature are constant, the ratio of their partial pressures is equal to the ratio of their moles, which is 2 : 1.

8Which of the following statements regarding the Maxwell-Boltzmann distribution of molecular speeds for a gas is correct?

A.As temperature increases, the peak of the curve shifts to the left and becomes broader.

B.The root-mean-square speed (v_rms) is always smaller than the most probable speed (v_mp).

C.As temperature increases, the fraction of molecules possessing the most probable speed decreases.

D.The average speed (v_avg) is given by the formula sqrt(3RT/M).

Explanation: As the temperature of a gas increases, the molecular speed distribution curve flattens out and shifts to the right (higher speeds). Because the curve broadens, the peak height decreases, which means that the fraction of molecules possessing the most probable speed decreases. The values of the speeds follow the order: v_mp < v_avg < v_rms, and the formula for average speed is sqrt(8RT/pi*M).

9One mole of an ideal gas expands isothermally and reversibly at 300 K from an initial volume of 10 L to a final volume of 100 L. What is the work done by the gas? (Take R = 8.314 J/mol-K, ln 10 = 2.303)

A.-5.74 kJ

B.+5.74 kJ

C.-2.30 kJ

D.-11.48 kJ

Explanation: For an isothermal reversible expansion of an ideal gas, the work done is given by W = -nRT ln(V_final / V_initial). Substituting the values: W = -(1 mol) * (8.314 J/mol-K) * (300 K) * ln(100/10) = -8.314 * 300 * ln(10) = -2494.2 * 2.303 J = -5744 J, or -5.74 kJ. The negative sign indicates work is done by the gas on the surroundings.

10For a spontaneous endothermic reaction occurring at constant temperature and pressure, which of the following thermodynamic relations must be true?

A.Delta S_sys < 0

B.Delta S_surr > 0

C.Delta S_universe > 0

D.Delta G_sys > 0

Explanation: According to the Second Law of Thermodynamics, any spontaneous process must result in an increase in the total entropy of the universe: Delta S_universe = Delta S_sys + Delta S_surr > 0. For an endothermic reaction (Delta H > 0), the system absorbs heat from the surroundings, meaning Delta S_surr = -Delta H/T < 0. For the reaction to be spontaneous, Delta G_sys must be negative (Delta G_sys < 0), which requires Delta S_sys to be positive and large enough to overcome the negative entropy change of the surroundings.

About the NSEC Exam

The National Standard Examination in Chemistry (NSEC) is the prestigious first stage of the Chemistry Olympiad selection process in India. Organized by the IAPT in collaboration with HBCSE, the exam is open to Indian high school students. It tests advanced chemistry concepts spanning Physical, Inorganic, and Organic Chemistry at a level significantly higher than standard school board curricula. Top performers qualify for the Indian National Chemistry Olympiad (INChO), leading to potential selection for the International Chemistry Olympiad (IChO).

Assessment

60 objective questions: Part A (48 single-correct, +3/-1 marks) and Part B (12 multi-correct, +6/0 marks)

Time Limit

2 hours

Passing Score

Minimum Admissible Score (MAS), typically 50% of the average of the top 10 scorers' marks

Exam Fee

₹300 (IAPT (Indian Association of Physics Teachers) and HBCSE (Homi Bhabha Centre for Science Education))

NSEC Exam Content Outline

35%

Physical Chemistry

Stoichiometry, atomic structure, ideal and real gases, thermodynamics, chemical kinetics, chemical and ionic equilibrium, electrochemistry, solutions, and solid state.

25%

Inorganic Chemistry

Chemical bonding, periodicity of properties, main group chemistry (s and p blocks), d-block and f-block transition elements, coordination chemistry, metallurgy, and salt analysis.

40%

Organic Chemistry

General organic chemistry (GOC), isomerism (structural and stereoisomerism), hydrocarbons, alkyl halides, oxygenates (alcohols, phenols, ethers, carbonyls, carboxylic acids), nitrogen derivatives, biomolecules, and polymers.

How to Pass the NSEC Exam

What You Need to Know

Passing score: Minimum Admissible Score (MAS), typically 50% of the average of the top 10 scorers' marks
Assessment: 60 objective questions: Part A (48 single-correct, +3/-1 marks) and Part B (12 multi-correct, +6/0 marks)
Time limit: 2 hours
Exam fee: ₹300

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

NSEC Study Tips from Top Performers

1Focus heavily on NCERT Class 11 and 12 Chemistry textbooks as the foundation, then build up to JEE Advanced resources.

2For Physical Chemistry, practice numericals on thermodynamics, equilibrium, and kinetics regularly to improve speed and accuracy.

3In Organic Chemistry, build a strong grasp of electronic effects (mesomeric, inductive) and study detailed mechanisms of named reactions.

4Practice drawing Molecular Orbital diagrams and VSEPR shapes for complex inorganic compounds.

5Work through previous years' NSEC question papers (PYQs) to understand the pattern and difficulty level of the questions.

6Familiarize yourself with the qualitative analysis (salt analysis) reactions, as they are frequently asked in the inorganic section.

Frequently Asked Questions

What is the NSEC?

The National Standard Examination in Chemistry (NSEC) is the first stage of the selection process for the International Chemistry Olympiad (IChO). It is organized by the Indian Association of Physics Teachers (IAPT) in collaboration with the Homi Bhabha Centre for Science Education (HBCSE).

What is the syllabus for the NSEC?

The syllabus is broadly equivalent to the Senior Secondary (Class XI and XII) Chemistry curriculum of the CBSE. However, the questions are designed to test deep conceptual understanding and problem-solving skills under novel conditions, making it significantly more difficult than regular board exams.

What is the exam pattern of NSEC?

The NSEC is a 2-hour offline paper containing 60 multiple-choice questions. It is divided into Part A (48 questions with only one correct option; +3 marks for correct, -1 for incorrect) and Part B (12 questions with one or more correct options; +6 marks for correct, 0 for incorrect).

How much is the registration fee?

The registration fee for the NSEC is ₹300 per subject. Once paid, no further fees are charged for subsequent stages (INChO, OCSC, etc.) if the candidate qualifies.

What is the Minimum Admissible Score (MAS)?

The MAS is the minimum score required to be considered for qualification to the second stage (INChO). It is calculated as 50% of the average of the scores of the top 10 candidates nationwide.

Who is eligible to participate in NSEC?

Indian students in Class 12 or below who meet the age requirements (typically 14-19 years) and have not yet completed their board exams are eligible to register. They must also be eligible to hold an Indian passport.