# Physics MCQs for Class 12 with Answers Chapter 12 Atoms

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Q.1. Balmer series lies in which spectrum?
(a) visible
(b) ultraviolet
(c) infrared
(d) partially visible, partially infrared

Q.2. In Bohr model of hydrogen atom, let P.E. represents potential energy and T.E. represents the total energy. In going to a higher level.
(a) P. E. decreases, T.E. increases
(b) P. E. increases, T.E. decreases
(c) P. E. decreases, T.E. decreases
(d) P. E. increases, T.E. increases

Q.3. Which of the following statements is correct in case of Thomson’s atomic model?
(a) It explains the phenomenon of thermionic emission, photoelectric emission and ionisation.
(b) It could not explain emission of line spectra by elements.
(c) It could not explain scattering of 􀁄-particles
(d) All of the above

Q.4. Which one did Rutherford consider to be supported by the results of experiments in which α-particles were scattered by gold foil?
(a) The nucleus of an atom is held together by forces which
are much stronger than electrical or gravitational forces.
(b) The force of repulsion between an atomic nucleus and
an α-particle varies with distance according to inverse
square law.
(c) α-particles are nuclei of Helium atoms.
(d) Atoms can exist with a series of discrete energy levels

Q.5. According to the Rutherford’s atomic model, the electrons inside the atom are
(a) stationary
(b) not stationary
(c) centralized
(d) None of these

Q.6. According to classical theory, the circular path of an electron in Rutherford atom model is
(a) spiral
(b) circular
(c) parabolic
(d) straight line

Q.7. Rutherford’s α-particle experiment showed that the atoms have
(a) Proton
(b) Nucleus
(c) Neutron
(d) Electrons

Q.8. Electrons in the atom are held to the nucleus by
(a) coulomb’s force
(b) nuclear force
(c) vander waal’s force
(d) gravitational force

Q.9. The Rutherford α-particle experiment shows that most of the α-particles pass through almost unscattered while some are scattered through large angles. What information does

(a) Atom is hollow.
(b) The whole mass of the atom is concentrated in a small
centre called nucleus
(c) Nucleus is positively charged
(d) All of the above

Q.10. In Rutherford’s α -particle scattering experiment, what will be correct angle for α scattering for an impact parameter b = 0 ?
(a) 90º
(b) 270º
(c) 0º
(d) 180º

Answer Answer: (d) When b = 0, scattering angle, θ = 180º

Q.11. In the ground state in …A… electrons are in stable equilibrium while in …B… electrons always experiences a net force. Here, A and B refer to
(a) Dalton’s theory, Rutherford model
(b) Rutherford’s model, Bohr’s model
(c) Thomson’s model, Rutherford’s model
(d) Rutherford’s model, Thomson’s model

Answer Answer: (c) In Thomson’s model, electrons are in stable equilibrium i.e., no force or no net force, while, in Rutherford’s model, there is always a centripetal force acting on electron towards nucleus.

Q.12. The significant result deduced from the Rutherford’s scattering experiment is that
(a) whole of the positive charge is concentrated at the centre of atom
(b) there are neutrons inside the nucleus
(c) α-particles are helium nuclei
(d) electrons are embedded in the atom

Answer Answer: (a) The significant result deduced from the Rutherford’s scattering is that whole of the positive charge is concentrated at the centre of atom i.e. nucleus.

Q.13. Electrons in the atom are held to the nucleus by
(a) coulomb’s force
(b) nuclear force
(c) vander waal’s force
(d) gravitational force

Q.14. In a Rutherford scattering experiment when a projectile of
charge Z1 and mass M1 approaches a target nucleus of
charge Z2 and mass M2, the distance of closest approach
is r0. The energy of the projectile is
(a) directly proportional to Z1 Z2
(b) inversely proportional to Z1
(c) directly proportional to mass M1
(d) directly proportional to M1 × M2

Q.15. According to classical theory, Rutherford’s atomic model is
(a) stable
(b) unstable
(c) meta stable
(d) both (a) and (b)

Q.16. Rutherford’s atomic model was unstable because
(a) nuclei will break down
(b) electrons do not remain in orbit
(d) electrons are repelled by the nucleus

Q.17. The electrons of Rutherford’s model would be expected to lose energy because, they
(a) move randomly
(b) jump on nucleus
(d) escape from the atom

Q.18. As one considers orbits with higher values of n in a hydrogen atom, the electric potential energy of the atom
(a) decreases
(b) increases
(c) remains the same
(d) does not increase

Q.19. Which of the following parameters is the same for all hydrogen-like atoms and ions in their ground states?
(b) Speed of the electron
(c) Energy of the atom
(d) Orbital angular momentum of the electron

Answer Answer: (d) The orbital angular momentum of electron is independent of mass of orbiting particle & mass of nuclei.

Q.20. The angular speed of the electron in the nth orbit of Bohr hydrogen atom is
(a) directly proportional to n
(b) inversely proportional to n
(c) inversely proportional to n2
(d) inversely proportional to n3

Q.21. According to Bohr’s model of hydrogen atom
(a) the linear velocity of the electron is quantised.
(b) the angular velocity of the electron is quantised.
(c) the linear momentum of the electron is quantised.
(d) the angular momentum of the electron is quantised.

Q.22. As the quantum number increases, the difference of energy between consecutive energy levels
(a) remain the same
(b) increases
(c) decreases
(d) sometimes increases and sometimes decreases.

Q.23. Which of the following in a hydrogen atom is independent of the principal quantum number n? (The symbols have their usual meanings).
(a) νn
(b) Er
(c) En
(d) νr

Q.24. According to the Bohr theory of H-atom, the speed of the
electron, its energy and the radius of its orbit varies with
the principal quantum number n, respectively, as

(a) 1/n, n2, 1/n2
(b) n, 1/n2, n2
(c) n, 1/n2, 1/n2
(d) 1/n, 1/n2, 1/n2

Q.25. In terms of Bohr radius r0, the radius of the second Bohr orbit of a hydrogen atom is given by
(a) 4 r0
(b) 8 r0
(c) √2 r0
(d) 2 r0

Answer Answer: (a) As r α n2 , therefore, radius of 2nd Bohr’s orbit = 4 r0

Q.26. When hydrogen atom is in its first excited level, it’s radius is
(a) four times, it ground state radius
(b) twice times, it ground state radius
(c) same times, it ground state radius
(d) half times, it ground state radius.

Answer Answer: (a) rn= ro.n2, where ro is radius of ground-state & rn is radius of nth state. (For first excited state n = 2).

Q.27. The angular momentum of the electron in hydrogen atom in the ground state is
(a) 2h
(b) h/2
(c) h/2π
(d) h/4π

Angular momentum, mvr = nh/2π
So in ground state, angular momentum = h/2π .

Q.28. When an atomic gas or vapour is excited at low pressure, by passing an electric current through it then
(a) emission spectrum is observed
(b) absorption spectrucm is observed
(c) band spectrum is observed
(d) both (b) and (c)

Q.29. The first spectral series was disscovered by
(a) Balmer
(b) Lyman
(c) Paschen
(d) Pfund

Answer Answer: (a) In 1885, the first spectral series were observed by a Swedish school teacher Johann Jakob Balmer, This series is called the Balmer series.

Q.30. When an electron jumps from the fourth orbit to the second orbit, one gets the
(a) second line of Paschen series
(b) second line of Balmer series
(c) first line of Pfund series
(d) second line of Lyman series

Answer Answer: (b) Jump to second orbit leads to Balmer series. When an electron Jumps from 4th orbit to 2nd orbit shall give rise to second line of Balmer series.

Q.31. The Balmer series for the H-atom can be observed
(a) if we measure the frequencies of light emitted when an excited atom falls to the ground state
(b) if we measure the frequencies of light emitted due to transitions between excited states and the first excited state
(c) in any transition in a H-atom
(d) None of these

Q.32. In Balmer series of emission spectrum of hydrogen, first four lines with different wavelength Hα Hβ Hγ and Hδ are obtained. Which line has maximum frequency out of these?
(a) Hα (b) Hβ (c) Hγ (d) Hδ

Answer Answer: (d) Since out of the given four lines H􀁇 line has smallest wavelength. Hence the frequency of this line will be maximum.

Q.33. In which of the following series, does the 121.5 nm line of the spectrum of the hydrogen atom lie ?
(a) Lyman series
(b) Balmer series
(c) Paschen series
(d) Brackett series.

Answer Answer: (a) Since 121.5 nm line of spectrum of hydrogen atom lies in ultraviolet region, therefore it is Lyman series.

Q.34. Which of the following series in the spectrum of hydrogen atom lies in the visible region of the electromagnetic spectrum?
(a) Paschen series
(b) Balmer series
(c) Lyman series
(d) Brackett series

Answer Answer: (b) Transition from higher states to n = 2 lead to emission of radiation with wavelengths 656.3 nm and 365.0 nm. These wavelengths fall in the visible region and constitute the Balmer series.

Q.35. The shortest wavelength in Balmer’s series for Hydrogen atom is …A… and this is obtained by substituting …B … in Balmer’s formula. Here, A and B refer to
(a) 656.3 nm, n = 3
(b) 486.1 nm, n = 4
(c) 410.2 nm, n = 5
(d) 364.6 nm, n = ∞

Answer Answer: (d) The shortest wavelength occurs when an electron makes a transitions from n = ∞ to n = 2 state.

Q.36. As an electron makes a transition from an excited state to the ground state of a hydrogen – like atom/ion
(a) kinetic energy decreases, potential energy increases but total energy remains same
(b) kinetic energy and total energy decrease but potential energy increases
(c) its kinetic energy increases but potential energy and total energy decrease
(d) kinetic energy, potential energy and total energy decrease

Q.37. Which of the following series in the spectrum of hydrogen atom lies in the visible region of the electromagnetic spectrum?
(a) Paschen series
(b) Balmer series
(c) Lyman series
(d) Brackett series

Answer Answer: (b) Transition from higher states to n = 2 lead to emission of radiation with wavelengths 656.3 nm and 365.0 nm. These wavelengths fall in the visible region and constitute the Balmer series.

Q.38. In a hydrogen atom, which of the following electronic transitions would involve the maximum energy change
(a) n = 2 to n = 1
(b) n = 3 to n = 1
(c) n = 4 to n = 2
(d) n = 3 to n = 2

Q.39. Hydrogen atom excites energy level from fundamental state to n = 3. Number of spectral lines according to Bohr, is
(a) 4
(b) 3
(c) 1
(d) 2

Q.40. The transition from the state n = 4 to n = 3 in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from
(a) 2 → 1
(b) 3 → 2
(c) 4 → 2
(d) 5 → 4

Q.41. For a given value of n, the number of electrons in an orbit is
(a) n
(b) n2
(c) 2n2
(d) 2n

Q.42. Bohr’s atom model is the modification of Rutherford’s atom model by the application of
(a) newton’s theory
(b) huygen’s theory
(c) maxwell’s theory
(d) planck’s quantum theory

Q.43. In Bohr’s model electrons are revolving in a circular orbits around the nucleus called as
(a) stationary orbits
(c) Bohr’s orbits
(d) all of these

Q.44. According to Bohr’s theory of H atom, an electron can revolve around a proton indefinitely, if its path is
(a) a perfect circle of any radius
(b) a circle of an allowed radius
(c) a circle of constantly decreasing radius
(d) an ellipse with fixed focus

Q.45. According to Bohr the difference between the energies of the electron in the two orbits is equal to
(a) hν
(b) hc/λ
(c) both (a) and (b)
(d) neither (a) nor (b)

Q.46. The angular momentum of electrons in an atom produces
(a) magnetic moment
(b) ZEEMAN effect
(c) light
(d) nuclear fission

Q.47. According to Planck’s quantum theory any electromagnetic radiation is
(a) continuously emitted
(b) continuously absorbed
(c) emitted or absorbed in discrete units
(d) None of these