CBSE Class 12 Physics MCQs for Atoms Chapter 12

CBSE Class 12 Physics MCQs for Chapter 12: Understanding the concept of atoms is very important part of Class 12 Physics. This topic deals with the structure, energy levels, and emission or absorption of light by atoms. The CBSE Class 12 Physics MCQs for Chapter 12 are carefully designed to help students practice key concepts in easy and effective way. These atoms class 12 mcq questions follow the official CBSE Class 12 Physics Syllabus and support deeper understanding through problem solving.

Students looking for atoms mcq class 12 pdf or online atom class 12 mcq physics practice can use this material for self-study and quick revision before class 12 exams. Each multiple-choice question is framed based on NCERT Solutions for Class 12 Physics and other exam-oriented resources. In this chapter, learners will explore how atom models evolved from Rutherford to Bohr model, energy quantization, spectra, and much more.

Practicing atoms mcq class 12 helps improving accuracy and conceptual clarity. Remember, small daily practice from such MCQs Questions builds strong base for CBSE Class 12 Boards as well as competitive exams like NEET Exam and JEE Exam.

Atoms Class 12 Chapter 12 MCQs Questions with Answers

Check the multiple-choice questions for the 12th Class Physics chapter on Atoms. Each question offers four options, with only one correct answer. Students should select the correct option and then verify their answers provided.

Que 1. A spectral line is emitted when an electron

(A) jumps from lower orbit to higher orbit

(B) jumps from higher orbit to lower orbit

(C) rotates in a circular orbit

(D) rotates in an elliptical orbit

Ans: (B)

Emission occurs when electron falls from higher to lower energy level.

Que 2. The ionisation potential of hydrogen is 13.6 eV. The energy of the atom in n = 2 state will be

(A) –10.2 eV

(B) –6.4 eV

(C) –3.4 eV

(D) –4.4 eV

Ans: (C)

Energy at level n is Eₙ = –13.6/n². For n = 2 → –3.4 eV.

Que 3. In Bohr’s model, the angular momentum of the electron is quantized and equals

(A) n h

(B) n h / 2π

(C) h

(D) h / 2π

Ans: (B)

Bohr postulate: mvr = nħ = n h / 2π.

Que 4. If the Bohr radius (first orbit radius) is a₀, then the radius of the third orbit is

(A) a₀/9

(B) a₀

(C) 9a₀

(D) 3a₀

Ans: (C)

rₙ = n²a₀ → r₃ = 9a₀.

Que 5. In Bohr’s hydrogen atom, kinetic energy of the electron is proportional to

(A) 1/r

(B) 1/r²

(C) r

(D) r²

Ans: (A)

K = e² / (8π ε₀ r) → proportional to 1/r.

Que 6. The longest wavelength in the Balmer series of hydrogen’s spectrum is

(A) 6563 Å

(B) 1216 Å

(C) 4800 Å

(D) 5600 Å

Ans: (A)

Transition 3→2 gives 6563 Å (Hα line).

Que 7. The wave number of the first Balmer line (in terms of Rydberg constant R) is

(A) R

(B) 3R

(C) 5R/36

(D) 8R/9

Ans: (C)

ν̃ = R(1/2² − 1/3²) = 5R/36.

Que 8. For hydrogen-like atom, energy difference between 3rd and 4th orbits is

(A) 3.40 eV

(B) 1.51 eV

(C) 0.85 eV

(D) 0.66 eV

Ans: (D)

ΔE = 13.6(1/3² − 1/4²) = 0.66 eV.

Que 9. For an atom with atomic number Z, energy of electron in nth orbit is

(A) –13.6 Z²/n² eV

(B) –13.6 / (Z²n²) eV

(C) –13.6 Z/n eV

(D) –13.6 / n eV

Ans: (A)

Eₙ = –13.6 Z² / n² eV.

Que 10. As n increases, the energy gap between consecutive orbits

(A) decreases

(B) increases

(C) first decreases then increases

(D) remains constant

Ans: (A)

Higher levels get closer together as n rises.

Que 11. In Rutherford’s experiment, if 232 counts/min at 60°, the count at 120° is

(A) 232

(B) 116

(C) 26

(D) 52

Ans: (C)

Scattering intensity ∝ 1/sin⁴(θ/2), count drops sharply at large angles.

Que 12. Two electrons move in circular orbits of radii R and 4R. Ratio of periods (T₁:T₂) is

(A) 1/8

(B) 1/4

(C) 4

(D) 8

Ans: (A)

T ∝ n³, radius ∝ n² → T₂ = 8T₁, so ratio = 1/8.

Que 13. Ratio of energies of hydrogen atom in first and second excited states is

(A) 1/4

(B) 4/9

(C) 9/4

(D) 4

Ans: (C)

E ∝ 1/n² → (1/2²):(1/3²)=9:4.

Que 14. Ratio of period of revolution for n=1 and n=2 is

(A) 1/2

(B) 1/4

(C) 1/8

(D) 2

Ans: (C)

T ∝ n³ → T₁:T₂ = 1:8.

Que 15. Radius of nth orbit in Bohr model (atomic number Z) is proportional to

(A) Z²n²

(B) Z²/n²

(C) Z²/n

(D) n²/Z

Ans: (D)

rₙ = a₀ n²/Z.

Que 16. Electron jumps from 3rd to 2nd orbit. Wavelength λ of emitted radiation is

(A) 36/5R

(B) 5/36R

(C) 5/R

(D) R/6

Ans: (A)

1/λ = R(1/2² − 1/3²) = 5R/36 → λ = 36/5R.

Que 17. Fine structure of hydrogen spectral lines arises due to

(A) Finite nucleus size

(B) Neutrons

(C) Spin–orbit coupling

(D) Orbital angular momentum only

Ans: (C)

Due to interaction between electron spin and orbital motion.

Que 18. Ratio of energy in first to second orbit (hydrogen)

(A) 1/4

(B) 1/2

(C) 2

(D) 4

Ans: (D)

|E₁|:|E₂| = 13.6:3.4 = 4:1.

Que 19. When an electron jumps to the innermost orbit, spectral line belongs to

(A) Lyman

(B) Balmer

(C) Paschen

(D) Pfund

Ans: (A)

Transition to n=1 → Lyman (UV region).

Que 20. For non-radiating stationary orbit in Bohr’s model, condition is

(A) Angular momentum = n h

(B) Orbit must be circular

(C) Orbit must be elliptical

(D) None of these

Ans: (A)

mvr = n ħ (quantized angular momentum).