Stop Reading. Start Scoring.

Sections 1 to 12 taught you the chapter. This section finds out whether you can use it under a clock, which is a completely different skill. There is no new theory here — just 30 questions built to the JEE Main pattern on Structure of Atom, and a marking scheme that punishes the thing students do most: guessing.

The rules of engagement

Key Point: Do not treat this as a reading exercise. Sit down with a blank sheet, a pen and a timer, and attempt all 30 questions in one unbroken sitting before you look at a single explanation.

The setup What it is
Number of questions 30 (26 single-correct MCQs + 4 numerical-value-type questions, all given with four options here)
Marking scheme +4+4 correct, −1-1 incorrect, 00 unattempted
Maximum score 30×4=12030 \times 4 = 120 marks
Minimum possible score 30×(−1)=−3030 \times (-1) = -30 marks
Suggested time limit 35 minutes (JEE Main pace is about 1 minute per question)
Allowed rough sheet, your own brain, and these constants: h=6.626×10−34 J sh = 6.626 \times 10^{-34}\ \mathrm{J\ s}, c=3.0×108 m s−1c = 3.0 \times 10^{8}\ \mathrm{m\ s^{-1}}, me=9.1×10−31m_e = 9.1 \times 10^{-31} kg, e=1.602×10−19e = 1.602 \times 10^{-19} C, NA=6.022×1023N_A = 6.022 \times 10^{23}, RH=2.18×10−18R_H = 2.18 \times 10^{-18} J =13.6= 13.6 eV, Rydberg constant 109,677 cm−1109{,}677\ \mathrm{cm^{-1}}, a0=0.529a_0 = 0.529 Å =52.9= 52.9 pm, v1=2.18×106 m s−1v_1 = 2.18 \times 10^{6}\ \mathrm{m\ s^{-1}}, and the shortcut hc=1240hc = 1240 eV nm
Not allowed calculator, formula sheet, looking back at Sections 1 to 12

Unless a question says otherwise, treat every hydrogen-like ion with the Bohr formulae En=−13.6 Z2/n2E_n = -13.6\,Z^2/n^2 eV, rn=0.529 n2/Zr_n = 0.529\,n^2/Z Å and vn=2.18×106 Z/nv_n = 2.18 \times 10^{6}\,Z/n m s−1^{-1}, and take the Rydberg formula as νˉ=109,677(1n12−1n22)Z2 cm−1\bar{\nu} = 109{,}677\left(\frac{1}{n_1^2} - \frac{1}{n_2^2}\right)Z^2\ \mathrm{cm^{-1}}. Where a rounded constant would change the option you pick, the question tells you which value to use.

[Exam Tip] That −1-1 is not decoration. In the real paper, four wild guesses that produce one lucky hit earn you 4−3=+14 - 3 = +1 mark for four minutes of work — a terrible trade. But a question you have narrowed down to two options is worth attempting: on average that gives 4−12=+1.5\frac{4 - 1}{2} = +1.5 marks per attempt. Narrow first, then commit. Leave blank only what you cannot narrow at all. For the numerical-value-type questions there is no negative marking in the actual JEE Main paper, but we keep −1-1 here on purpose — it forces you to check your arithmetic instead of typing the first number you get.

What this set covers

Topic map and self-scoring card for the 30-question JEE Main atom drill

Topic Questions How many
Sub-atomic particles, isotopes, isobars and isoelectronic species Q1 to Q3 3
Electromagnetic radiation, photon energy and the photoelectric effect Q4 to Q7 4
Bohr model: radius, velocity, energy and frequency of H-like species Q8 to Q13 6
Hydrogen spectrum: line counting, series limits and matching transitions Q14 to Q17 4
de Broglie wavelength and the uncertainty principle Q18 to Q20 3
Quantum numbers, orbital counting, nodes, angular momentum and shapes Q21 to Q25 5
(n+l)(n + l) ordering, electronic configurations, unpaired electrons, magnetic moment and ZeffZ_{\text{eff}} Q26 to Q30 5

That spread is deliberate — it mirrors how JEE Main actually samples this chapter. The Bohr model, the hydrogen spectrum and the quantum-number block together account for 15 of the 30 questions, because in the real paper those three ideas carry most of what gets asked from Structure of Atom, with one photoelectric or de Broglie numerical and one configuration-or-magnetic-moment question almost every year. The difficulty mix is roughly 20% easy, 50% medium and 30% hard, so do not panic if a few feel brutal; they are meant to. Questions 14, 15, 22 and 29 are written in the numerical-value style: the answer is a number you must compute exactly, and the four options are there only so you can mark yourself.

Scoring Yourself Honestly

Mark your sheet with the real scheme — +4+4, −1-1, 00 — and total it. Do not award yourself half marks for "I knew that one really" or "I only forgot to square the ZZ". The number you get is the number that matters.

The bands

Your score (out of 120) Verdict What to do next
96 to 120 Exam ready. You are at 80% or above on a hard set. Move on. Structure of Atom will not cost you marks. Revisit only the specific questions you missed.
72 to 95 Solid, but leaking marks. These are almost always slips, not gaps — ZZ used where Z2Z^2 was needed, n(n−1)/2n(n-1)/2 applied when the electron never reaches the ground state, a wavelength reported in cm instead of nm. Redo every wrong question without looking at the explanation first.
44 to 71 Shaky. The ideas are there; the execution is not. For each wrong answer, go back to the section it came from (use the topic map above) and re-work its solved examples before re-attempting.
Below 44 Start again. Work through Sections 1 to 10 properly, then Section 11's solved examples, then come back. Re-attempting this set now teaches you nothing.

Read your own answer sheet

Before you touch the explanations, sort your mistakes into three piles. This is the most valuable ten minutes in the whole section.

  1. Concept errors — you did not know that kinetic energy is −En-E_n and potential energy is 2En2E_n in a Bohr orbit, or that the number of radial nodes is n−l−1n - l - 1 and not n−ln - l, or that msm_s can only be +12+\frac{1}{2} or −12-\frac{1}{2}. Fixable by revision, and quickly.
  2. Execution errors — right method, wrong arithmetic: you wrote 19−116\frac{1}{9} - \frac{1}{16} as 7144\frac{7}{144} and then inverted it upside down, or multiplied by ZZ instead of Z2Z^2 in the energy formula, or dropped a factor of 10−910^{-9} when converting nm to m. Fixable by slowing down for four seconds at the last step.
  3. Reading errors — you found the number of lines to the ground state when the question stopped the electron at n=2n = 2, or reported the energy of the orbit when the question asked for the ionisation energy from it, or counted orbitals when it asked for electrons. These are the cheapest marks in the paper to win back, and the ones students refuse to take seriously.

Key Point: A student who scores 76 with three concept errors is in far better shape than one who scores 76 with nine reading errors. The first has three things to learn. The second has a habit to break, and habits take longer.

[Exam Tip] Every explanation below is written as a full step-by-step solution, so this set doubles as revision material. Read the explanation even for the questions you got right — sometimes you got there the slow way, and the fast way (E=1240/λE = 1240/\lambda in eV with λ\lambda in nm, r∝n2/Zr \propto n^2/Z, "count the unpaired electrons, then n(n+2)\sqrt{n(n+2)}") is what you will need in the exam hall.