Atoms: Class 12 Previous Year Questions

Atoms questions asked in CBSE board exams

Repeated questions first. Open the free app to see each question as it appeared in the paper, with its marking scheme.

1. ( ) 12. In Bohr model of hydrogen atom, the electron makes a transition from n = 5 to n = 1 state. As a result, a photon of wavelength  is emitted in the process. The wavelength of the photon emitted when an electron makes a transition from energy level n = 5…
   Board 20261 markAssertion-Reason
2.  4. In Bohr model of hydrogen atom, for large values of n, the distance between the consecutive orbits is proportional to 1 (A) n (B) n (C) n2 (D) n3 { } 6  5. y-         1A   –y            …
   Board 20261 markMCQ
3. (a) State Bohr’s second postulate and mention its significance. 3 (b) Prove that, in Bohr model of hydrogen atom as principal quantum number n becomes large, the energy levels get closer and closer.
   Board 20263 marksshort answer
4.  16. Reason (A) : In Bohr model of hydrogen atom, the energy levels are discrete and quantised. 1 Reason (R) : In a hydrogen atom, the electrostatic force on the electron provides the necessary centripetal force to it to revolve around the nucleus. { } 12  …
   Board 20261 markvery short
5. Assertion (A) : In Bohr model of hydrogen atom, the angular momentum of an electron in nth orbit is proportional to the square root of its orbit radius rn Reason (R) : According to Bohr model, electron can jump to its nearest orbits only.
   Board 20251 markAssertion-Reason
6. Prove that, in Bohr model of hydrogen atom, the time period of revolution of an electron in nth orbit is proportional to n3. Page 11 of 24 21Si-3 5107 22. (a)3 3V60.20.4 (i) (i) 3 alr ·(h (t) (b) (i) 24.a· () B2 ·· 25. (a) (b) I lye lharlho i bp h Page 12 of 2…
   Board 20252 marksshort answer
7. The energy of an electron in a hydrogen atom in ground state is -13.6 eV. Its energy in an orbit corresponding to quantum number n is -0.544 eV. The value of n is (A) 2 (B) 3 (C) 4 (D)
   Board 20251 markMCQ
8. Assertion (A) : The potential energy of an electron revolving in any stationary orbit in a hydrogen atom is positive. Reason(R) : The total energy of a charged particle is always positive.
   Board 20251 markAssertion-Reason
9. Atomic spectral emission lines of hydrogen atom are incident on a zinc surface. The lines which can emit photoelectrons from the surface are members of (A)Balmer series (B)Paschen series (C) Lyman series (D) Neither Balmer, nor Paschen nor Lyman series Page 7 …
   Board 20251 markMCQ
10. The transition of electron that gives rise to the formation of the second spectral line of the Balmer series in the spectrum of hydrogen atom corresponds to : (A) nf = 2 and ni = 3 (B) nf = 3 and ni = 4 (C) nf = 2 and ni = 4 (D) nf = 2 and ni =
    Board 20241 markMCQ
11. l. A hydrogen atom makes a transition from n = 5 to n = 1 orbit. The wavelength of photon emitted is 2. The wavelength of photon emitted when it makes a transition from n = 5 to n = 2 orbit is 16 (a) (b) 24 32 (c) (d) Page 7 of 24 (a) (b) (c) (d) 13.41020 1.2 …
    Board 20231 markMCQ
12. dmoëQ>oO H$m H$moB© ac òmoV loUr _| {H$gr p-n g§{Y S>m`moS> Am¡a bmoS> à{VamoYH$ go g§`mo{OV h¡ & bmoS> à{VamoY Ho$ {gam| na {ZJ©V dmoëQ>Vm Ho$ {bE ghr {dH$ën hmoJm : 10. The radius of the nth orbit in Bohr model of hydrogen atom is proportional to : (a) 2 n 1…
    Board 20231 markMCQ
13. Each of the statements below are based on the properties of electron orbits in a hydrogen atom. Identify a statement that correctly satisfies the Bohr’s model of an atom. A. The angular momentum of the orbiting electron is 3h/π. B. The potential energy of the …
    CBSE practice 2022-231 markMCQ
14. Assertion: According to Bohr’s atomic model the ratio of angular momenta of an electron in first excited state to that in ground state is 2:1. Reason: According to Bohr’s theory the angular momentum of the electron is directly proportional to the principal qua…
    CBSE practice 2023-241 markAssertion-Reason
15. (a) What is the ratio of minimum to maximum energy of the radiations emitted by transition of an electron to the ground state of a hydrogen atom? (b) As per de Broglie’s explanation of Bohr’s quantization condition of an orbiting electron, represent a schemati…
    CBSE practice 2021-223 marksshort answer
16. a. A glass container contains hydrogen atoms with all its atoms in their ground states. The container is irradiated with electromagnetic waves containing 3 wavelengths corresponding to Lyman, Balmer and Paschen series. The electromagnetic waves exiting the gla…
    CBSE practice 2022-233 marksshort answer
17. (a) Compare the de Broglie wavelength associated with the electron in the third orbit to the circumference of the orbit. (b) In which of the following will the electrons have the same de Broglie wavelength? (i) Third orbit of He atom (ii) Fourth orbit of He at…
    CBSE practice 2023-243 marksshort answer
18. (a) An electron of mass m and a photon carry the same energy E. What is the ratio of de Broglie wavelength associated with the electron to the wavelength of the photon? (b) Why do macroscopic objects in our daily life not show wave-like properties whereas in t…
    CBSE practice 2021-222 marksshort answer
19. Two like charges +q and +q are placed at a distance d. What work must be done by an external agent to bring another charge +q from infinity to the midpoint of the line joining the two given charges? 2 20(A) A certain magnetic substance is found to have a relat…
    Sample paper 2026-272 marksshort answer
20. An electron of mass m orbiting around a nucleus has an angular momentum L. The magnetic field produced by the electron at the center of the orbit of radius r can be expressed as (a) (b) (c) (d)
    CBSE practice 2023-241 markMCQ

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