KENDRIYA VIDYALAYA SANGATHAN
AHMEDABAD REGION
OBJECTIVE TYPE QUESTIONS
SUB: PHYSICS CHAPTER: ATOM CLASS : XII
MULTIPLE CHOICE QUESTIONS
1. When alpha particles are sent through a thin gold foil, most of them go straight through the
foil, because:
A) alpha particles are positively charged.
B) the mass of an alpha particle is more than the mass of an electron.
C) most of the part of an atom is empty space.
D) alpha particles move with high velocity.
2. Two H atoms in the ground state collide in-elastically. The maximum amount by which their
combined kinetic energy is reduced is
A) 10.20 eV
B) 20.40 eV
C) 13.6 eV
D) 27.2 eV
3. The Volume of an atom is of the order of
A) 10-10 m3
B) 10-15 m3
C) 10-30 m3
D) 10-45 m3
4. The ratio between total acceleration of the electron on singly ionized helium atom and
hydrogen atom (both in ground state) is
A) 4
B) 1
C) 8
D) 16
5. A beryllium atom is stripped of all but one of its electrons. What is the energy of the ground
state?
A) 213.6 eV
B) 2218 eV
C) 2122 eV
D) 240.8 eV
6. A photon beam of energy 12.1 eV is incident on a hydrogen atom. The orbit to which
electron of H-atom be excited is:
A) 2nd
B) 3rd
C) 4th
D) 5th
13.6
7. The energy of an electron in nth orbit of hydrogen atom is, En = − eV. The negative sign
n2
of energy indicates that:
A) electron is free to move.
B) electron is bound to the nucleus.
C) kinetic energy of electron is equal to potential energy of electron.
D) atom is radiating energy
8. Energy levels A, B, C of a certain atom corresponding to
increasing values of energy i.e., EA < EB < bEC. If λ1, λ2, λ3 are the
wavelengths of radiations corresponding to the transitions C to B,
B to A and C to A respectively, which of the following statements is
correct:
A) λ3 = λ1 + λ2
λ λ
B) λ3 = λ 1+λ2
1 2
C) λ1 + λ2 + λ3 = 0
D) 𝜆23 = 𝜆12 + 𝜆22
9. If in nature there may not be an element for which the principal quantum number n > 4, then
the total possible number of elements will be
A) 60
B) 32
C) 4
D) 64
10. If in hydrogen atom, radius of n th Bohr orbit is rn , frequency of revolution of electron in n th
orbit is fn choose the correct option
A)
B)
C)
D) Both (a) and (b)
11. The total energy of an electron in the first excited state of hydrogen atom is about -3.4 eV.
Its kinetic energy in this state is
A) 3.4 eV
B) 6.8 eV
C) -3.4 eV
D) -6.8 eV
12. The ratio of wavelength of the last line of Balmer series and the last line of Lyman series
A) 1
B) 4
C) 0.5
D) 2
13. An electron jumps from the 4th orbit to the 2nd orbit of hydrogen atom. Given the Rydberg’s
constant R = 105 cm-1. The frequency in Hz of the emitted radiation will be
3
A) 16 𝑥 105
3
B) 16 𝑥 1015
9
C) 16 𝑥 1015
3
D) 4 𝑥 1015
14. An electron in hydrogen atom makes a transition n1--> n2 where n1 and n2 are principal
quantum numbers of the two states. Assuming Bhor’s model to be valid, the time period of
the electron in the initial state is eight times that in the final state. The possible values of n1
and n2 are
A) n1 = 6 and n2 = 2
B) n1 = 8 and n2 = 1
C) n1 = 8 and n2 = 2
D) n1 = 4 and n2 = 2
15. According to Bohr's theory the moment of momentum of an electron revolving in second orbit
of hydrogen atom will be
A) 2ᴨ h
B) ᴨ h
ℎ
C) ᴨ
2ℎ
D) ᴨ
16. Energy of an electron in an excited hydrogen atom is -3.4 eV. Its angular momentum will be
A) 3.72 x 10-34 Js
B) 2.10 x 10-34 Js
C) 1.51 x 10-34 Js
D) 4.20 x 10-34 Js
17. The shortest wavelength in the Lyman series is 911.6 Å. Then the longest wavelength in the
Lyman series is
A) 1215 Å
B) ∞
C) 2430 Å
D) 3600 Å
18. In the Bohr model of the hydrogen atom, the ratio of the kinetic energy to the total energy of
the electron in a quantum state n is
A) – 1
B) + 1
1
C) 𝑛
1
D) 𝑛2
19. An electron is the hydrogen atom jumps from excited state n to the ground state. The
wavelength so emitted illuminates a photosensitive material having work function 2.75 eV. If
the stopping potential of the photo electron is 10 V, then the value of n is:
A) 5
B) 20
C) 3
D) 4
20. Some energy levels of a molecule are shown in the figure. The ratio of the
wavelengths r=λ1/λ2, is given by :
A) r = 1/3
B) r = 4/3
C) r = 2/3
D) r = 3/4
ASSERTION/REASON TYPE QUESTIONS
21. Assertion: Electrons in the atom are held due to coulomb forces.
Reason: The atom is stable only because the centripetal force due to Coulomb’s law is
balanced by
the centrifugal force.
A) Both Assertion and Reason are true, and the Reason is the correct explanation of the
Assertion.
B) Both Assertion and Reason are true, but the Reason is not the correct explanation of the
Assertion.
C) Assertion is true, but Reason is false.
D) Both Assertion and Reason are false.
22. Assertion: Because any two given energy levels, the number of absorption transitions is
always less than the number of emission transitions.
Reason: Absorption transitions start from the lowest energy level only and may end at any
higher energy level. But emission transitions may start from any higher energy level and end at
any energy level below it.
A) Both Assertion and Reason are true, and the Reason is the correct explanation of the
Assertion.
B) Both Assertion and Reason are true, but the Reason is not the correct explanation of the
Assertion.
C) Assertion is true, but Reason is false.
D) Both Assertion and Reason are false.
23. Assertion: Most of the mass of the atom is concentrated in its nucleus.
Reason: All alpha particles striking a gold sheet are scattered in different directions.
A) Both Assertion and Reason are true, and the Reason is the correct explanation of the
Assertion.
B) Both Assertion and Reason are true, but the Reason is not the correct explanation of the
Assertion.
C) Assertion is true, but Reason is false.
D) Both Assertion and Reason are false.
24. Assertion: Hydrogen atom consists of only one electron but its emission spectrum has
many lines.
Reason: Only Lyman series is found in the absorption spectrum of hydrogen atom whereas
in the
emission spectrum, all the series are found.
A) Both Assertion and Reason are true, and the Reason is the correct explanation of the
Assertion.
B) Both Assertion and Reason are true, but the Reason is not the correct explanation of the
Assertion.
C) Assertion is true, but Reason is false.
D) Both Assertion and Reason are false.
25. Assertion: In alpha particle scattering number of alpha particles undergoing head on
collision is small.
Reason: Small fraction of the number of incident particles rebound back.
A) Both Assertion and Reason are true, and the Reason is the correct explanation of the
Assertion.
B) Both Assertion and Reason are true, but the Reason is not the correct explanation of the
Assertion.
C) Assertion is true, but Reason is false.
D) Both Assertion and Reason are false.
26. Assertion: For the scattering of a-particles at a large angles, only the nucleus of the atom
is responsible.
Reason: Nucleus is very heavy in comparison to α particle.
A) Both Assertion and Reason are true, and the Reason is the correct explanation of the
Assertion.
B) Both Assertion and Reason are true, but the Reason is not the correct explanation of the
Assertion.
C) Assertion is true, but Reason is false.
D) Both Assertion and Reason are false.
CASE BASED QUESTIONS
27. The energy levels of a hypothetical single electron atom are shown below:
n = ∞ ………………………………………………………………… 0 eV
n = 5 …………………………………………………………………- 0.80 eV
n=4 …………………………………………………………………- 1.41 eV
n=3 …………………………………………………………………- 3.08 eV
n=2 …………………………………………………………………- 5.30 eV
n=1 …………………………………………………………………- 15.6 eV
i ) Find the amount of energy required to remove an electron from an isolated atom of the
atom.
A) 11.2 eV
B) 13.5 eV
C) 15.6 eV
D) 12.6 eV
ii) Find the short wavelength limit of the series terminating at n = 2
A) 3256 Å
B) 2339 Å
C) 2509 Å
D) 3494 Å
iii) Find the excitation potential energy for the state n = 3
A)14.64 eV
B) 9.93 eV
C)12.52 eV
D)10.04 eV
iv) Find the wave number of the photon emitted for the transition n = 3 to n = 1
A) 2.23 x 107 m-1
B) 1.009 x 107 m-1
C) 3.005 x 106 m-1
D ) 0.432 x 106 m-1
28. The spectral series of hydrogen atom were accounted for by Bohr using the relation
1 1 1
= 𝑅 [𝑛 2 + 𝑛 2 ]
𝜆 1 2
where, R=Rydberg constant = 1.097 x 107 m-1
Lyman series is obtained when an electron jumps to first orbit from any subsequent orbit.
Similarly, Balmer series is obtained when an electron jumps to 2 nd orbit from any subsequent
orbit. Paschen series is obtained when an electron jumps to 3 rd orbit from any subsequent orbit.
Whereas Lyman series in U.V. region, Balmer series is in visible region and Paschen series
lies in infrared region. Series limit is obtained when n2=∞.
i ) The wavelength of first spectral line of Lyman series is
A) 1215.4 Å
B) 1215.4 cm
C) 1215.4 m
D) 1215. 4 mm
ii ) The wavelength limit of Lyman series is
A) 1215.4 Å
B) 511.9 Å
C) 951.6 Å
D) 911.6 Å
iii) The frequency of first spectral line of Balmer series is
A) 1.097 x 107 Hz
B) 4.57 x 1014 Hz
C) 4.57 x 1015 Hz
D) 4.57 x 1016 Hz
iv) Which of the following transitions in hydrogen atom emit photon of highest frequency?
A) n=1 to n=2
B) n=2 to n=6
C) n=6 to n=2
D) n=2 to n=1
29. Teacher taught the Rutherford alpha scattering experiment in class. His teacher explained
that in alpha scattering experiment Rutherford concluded that most of the space within the
atom is empty. The entire positive charge and most of the mass of the atom is concentrated
in its central core. Trajectory of alpha particle depends on impact parameter which is the
perpendicular distance of the initial velocity vector of the alpha particle from the Centre of
the nucleus The extent of scattering is inversely proportional to the impact parameter.
i ) The least distance at which an alpha particle stops before reaching the nucleus is called:
A) Distance of scattering
B) Distance of rebounding
C) Distance of closest approach
D) Nuclear radius.
ii ) The alpha particles are emitted in this experiment by:
A) Charged helium
B) Electric cell
C) Gold foil of 0.01µm thickness
D) Radioactive source
iii) The perpendicular distance of velocity vector of approaching alpha particle from center of
target nucleus is
A) Scattering distance
B) impact parameter
C) trajectory
D) distance of closest approach
iv) The electrons revolve around the nucleus in
A) Orbit
B) Form the electron clouds
C) Both (a) & (b)
D) None of these
30. The Bohr model of the atom was proposed by Neil Bohr in 1915. It came into existence with
the modification of Rutherford’s model of an atom. Rutherford’s model introduced the
nuclear model of an atom, in which he explained that a nucleus (positively charged) is
surrounded by negatively charged electrons.
i ) Which of the following statements does not form a part of Bohr’s model of a hydrogen atom?
A) The energy of the electrons in the orbit is quantized
B) The electron in the orbit nearest the nucleus has the lowest energy
C) Electrons revolve in different orbits around the nucleus
D) The position and velocity of the electrons in the orbit cannot be determined simultaneously
ii ) What is in the center of the Rutherford model?
A) Single proton
B) Multiple electrons
C) A nucleus
D) Neutrons
iii) When an electron jumps from its orbit to another orbit, energy is:
A) emitted only
B) absorbed only
C) both (a) and (b)
D) none of these
iv) . What were the limitations of the Rutherford model which could not explain the observed
features of atomic spectra explained in Bohr’s model of a hydrogen atom?
A) It must emit a continuous spectrum
C) It loses its energy
D) Gaining its energy
E) A discrete spectrum
ANSWER KEY
1. C 7. B 13. C 19. D 25. B
2. A 8. B 14. C 20. A 26. A
3. C 9. A 15. C 21. A 27. (i) C (ii) B (iii) C (iv) B
4. C 10. D 16. B 22. A 28. (i) A (ii) D (iii) C (iv) A
5. B 11. A 17. A 23. C 29. (i) C (ii) A (iii) B (iv) A
6. B 12. B 18. A 24. A 30. (i) D (ii) C (iii) C (iv) D
