JEE (Main) · Chemistry, Class 11
Classification of Elements and Periodicity: JEE Main PYQ, 2020–2025
Classification of Elements and Periodicity (Chemistry, Class 11) has been asked 96 times in the 111 JEE (Main) shift papers from 2020–2025: about 0.9 questions a paper, 4% of all Chemistry questions. It is the 18th most-asked of 21 Chemistry chapters. The 2025 shifts had 15 from it in all. Last checked 28 October 2026.
Questions per year, all shifts
Year by year.
| Year | Questions |
|---|---|
| 2020 | 15in 14 papers |
| 2021 | 19in 26 papers |
| 2022 | 21in 24 papers |
| 2023 | 9in 12 papers |
| 2024 | 17in 18 papers |
| 2025 | 15in 17 papers |
JEE (Main) is sat in many shifts a year, each with its own paper; the counts add up every shift. 2021–2024 papers had 30 questions a subject, the others 25.
Inside the chapter
Topics asked most.
- Periodic trends43
- Ionization enthalpy24
- Modern periodic table16
- Electron gain enthalpy10
- Electronegativity3
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10 Classification of Elements and Periodicity questions to practise.
Our own questions, written in the JEE Main pattern and checked, each with an explanation. Pick an option to see the answer.
Q1 · Chemistry · Classification of Elements and Periodicity
The electron gain enthalpy of chlorine is −349 kJ mol⁻¹. Taking the Avogadro constant as 6.02 × 10²³ mol⁻¹, the energy released when one gaseous chlorine atom gains one electron is approximately:
Answer: (A)
The given value is per mole. Convert −349 kJ mol⁻¹ to −3.49 × 10⁵ J mol⁻¹, then divide by N_A = 6.02 × 10²³ mol⁻¹ to get one atom's energy change, about −5.8 × 10⁻¹⁹ J. The magnitude is the energy released per atom. Dividing by N_A is the step students most often skip.
Q2 · Chemistry · Classification of Elements and Periodicity
The first ionization enthalpy of beryllium (899 kJ mol⁻¹) is higher than that of boron (801 kJ mol⁻¹), although boron has the greater nuclear charge. Which statement correctly explains this?
Answer: (A)
In a multi-electron atom, orbitals of the same shell differ in energy because penetration decreases in the order s > p > d > f. Beryllium loses a 2s electron. Boron loses a 2p electron, which sits at higher energy and is partly shielded by the 2s electrons. This outweighs boron's extra proton, so the first ionization enthalpy of B is below that of Be.
Q3 · Chemistry · Classification of Elements and Periodicity
The electron gain enthalpy of chlorine is −349 kJ mol⁻¹. A sample of 3.55 g of gaseous Cl⁻ ions (take molar mass of Cl as 35.5 g mol⁻¹ and ignore the mass of electrons) is completely converted into gaseous Cl atoms by removing one electron from each ion. What is the energy change for this process?
Answer: (C)
Electron gain enthalpy is the enthalpy change when a gaseous atom gains an electron: Cl(g) + e⁻ → Cl⁻(g), ΔH = −349 kJ mol⁻¹. The reverse process, Cl⁻(g) → Cl(g) + e⁻, therefore has ΔH = +349 kJ mol⁻¹, so energy is absorbed. Moles of Cl⁻ = 3.55 g ÷ 35.5 g mol⁻¹ = 0.100 mol. Energy absorbed = 0.100 × 349 = 34.9 kJ.
Q4 · Chemistry · Classification of Elements and Periodicity
Which group of elements has a positive or near-zero electron gain enthalpy because its atoms have a completely filled ns² valence subshell?
Answer: (A)
Electron gain enthalpy depends on whether the incoming electron can enter an orbital that is partly empty. Groups 2 and 18 have filled ns² or ns²np⁶ valence shells, so the added electron must enter a higher energy level. This makes the value positive or near zero. Groups 13 to 17 still have vacancies, so their values are generally negative.
Q5 · Chemistry · Classification of Elements and Periodicity
The first ionization enthalpy of sodium is +496 kJ mol⁻¹ and the electron gain enthalpy of chlorine is −349 kJ mol⁻¹. What is the enthalpy change for Na(g) + Cl(g) → Na⁺(g) + Cl⁻(g)?
Answer: (D)
The overall process is the sum of two steps. First, Na(g) → Na⁺(g) + e⁻ absorbs +496 kJ/mol. Second, Cl(g) + e⁻ → Cl⁻(g) releases 349 kJ/mol. Adding them gives +496 − 349 = +147 kJ/mol. Forming gaseous ions from gaseous atoms is therefore endothermic, and in solid NaCl the lattice enthalpy supplies the stabilization.
Q6 · Chemistry · Classification of Elements and Periodicity
The first five successive ionization enthalpies (in kJ mol⁻¹) of a main-group element X are: IE₁ = 577, IE₂ = 1816, IE₃ = 2744, IE₄ = 11577, IE₅ = 14842. Which formula is the most probable for the stable chloride of X, assuming it is ionic?
Answer: (A)
Successive ionization enthalpies rise steadily while valence electrons are removed. A sudden, very large jump shows that the next electron comes from a inner shell with a noble-gas-like configuration. Here the ratios are IE₂/IE₁ ≈ 3.1, IE₃/IE₂ ≈ 1.5 and IE₄/IE₃ ≈ 4.2. The largest jump is after IE₃, so X has three valence electrons (Group 13, like Al). It forms X³⁺ and the chloride is XCl₃.
Q7 · Chemistry · Classification of Elements and Periodicity
An element has the outermost electronic configuration 5s². To which group of the long form of the periodic table does it belong?
Answer: (A)
In the s-block, group number equals the number of valence electrons (ns¹ gives group 1, ns² gives group 2). Here the configuration is 5s², so the element is in group 2 of period 5, which is strontium-type.
Q8 · Chemistry · Classification of Elements and Periodicity
The ionization enthalpy of a hydrogen atom in its ground state is 1312 kJ mol⁻¹. Using the hydrogen-like energy expression Eₙ ∝ −Z²/n², what is the energy needed to remove the remaining electron from one mole of ground-state Li²⁺ ions?
Answer: (D)
In a one-electron species the energy is Eₙ = −(2.18 × 10⁻¹⁸ J) Z²/n². Ionization from the ground state (n = 1) needs the energy of the level with the sign reversed, so it is proportional to Z². For hydrogen Z = 1 gives 1312 kJ mol⁻¹. For Li²⁺, Z = 3, so the value is 3² × 1312 = 9 × 1312 = 11 808 kJ mol⁻¹.
Q9 · Chemistry · Classification of Elements and Periodicity
Which of the following arranges Mg, Al, P and S in the correct order of increasing first ionisation enthalpy?
Answer: (A)
The general trend is an increase across a period, but two irregularities occur. (1) Group 2 to group 13: Mg removes a 3s electron, which penetrates well and is held tightly. Al removes a 3p electron, which is shielded by 3s² and is higher in energy. So Al < Mg (578 vs 738 kJ mol⁻¹). (2) Group 15 to group 16: P has the stable half-filled 3p³ configuration. S has 3p⁴, where a paired electron experiences inter-electronic repulsion and is removed more easily. So S < P (about 1000 vs 1012 kJ mol⁻¹). Combining both anomalies gives Al < Mg < S < P. The other options each ignore one or both of these irregularities.
Q10 · Chemistry · Classification of Elements and Periodicity
Which statement correctly compares the first ionisation enthalpies of nitrogen and oxygen in period 2?
Answer: (A)
Principle: ionisation enthalpy generally rises across a period as nuclear charge increases and atomic size decreases. The main exception in period 2 is that nitrogen's half-filled 2p³ configuration is unusually stable, so its first ionisation enthalpy (about 1402 kJ/mol) is higher than oxygen's (about 1314 kJ/mol). Apply the exception rather than the general rule.
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About Classification of Elements and Periodicity in JEE Main.
How many questions come from Classification of Elements and Periodicity in JEE Main?
Classification of Elements and Periodicity (Chemistry, Class 11) has been asked 96 times in the 111 JEE (Main) shift papers from 2020–2025: about 0.9 questions a paper, 4% of all Chemistry questions. It is the 18th most-asked of 21 Chemistry chapters. The 2025 shifts had 15 from it in all.
Which topics of Classification of Elements and Periodicity are asked most in JEE Main?
Periodic trends (43), Ionization enthalpy (24), Modern periodic table (16), Electron gain enthalpy (10), counted over the papers from 2020–2025.
Is Classification of Elements and Periodicity important for JEE Main 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 18 of 21 in Chemistry; use that to decide how much time it gets, not whether to study it.
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On Nikaalle, free: sign up and practise every past JEE Main question from Classification of Elements and Periodicity with an explanation for each, or sit the full papers timed. The ten questions on this page are our own, written in the same pattern.
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