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CHAPTER 12 ATOMS Exercise 1: NCERT Based Topic-wise MCQs 12.1 INTRODUCTION 1. Which of the following statements is correct in case of Thomson's atomic model? NCERT Page-414/ N-291 (a) It explains the phenomenon of thermionic emission, photoelectric emission and ionisation. (b) It could explain emission of line spectra by elements. (c) It could explain scattering of α-particles (d) All of the above 12.2 ALPHA-PARTICLE SCATTERING AND RUTHEFORD’S NUCLEAR MODEL OF ATOM 2. √d1 and √d2 are the impact parameters corresponding to scattering angles 60∘ and 90∘ . respectively, when an α particle is approaching a gold nucleus. For d1 = xd2, the value of x will be (a) 3 (b) 5 (c) 7 (d) 9 3. Rutherford's α-particle experiment showed that the atoms have NCERT Page-416/ N-293 (a) Proton (b) Nucleus (c) Neutron (d) (d) 4. Rutherford's atomic model NCERT Page-416/ N-293 (a) nuclei will break down (b) electrons do not remain in orbit (c) orbiting electrons radiate energy (d) electrons are repelled by the nucleus 5. As one considers orbits with higher values of n in a hydrogen atom, the electric potential energy of the atom (a) decreases NCERT Page-420/ N-293 (b) increases (c) remains the same (d) does not increase 6. The significant result deduced from the Rutherford's scattering experiment is that NCERT Page-416/ N-293 (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 7. When an α-particle of mass ' m ' moving with velocity ' v ' bombards on a heavy nucleus of charge 'Ze', its distance of closest approach from the nucleus depends on v as: NCERT Page-420/ N-295
(a) 1 v (b) 1 √v (c) 1 v 2 (d) v 8. In Rutherford's α-particle scattering experiment, what will be correct angle for α scattering for an impact parameter = 0 ? NCERT Page-418/ N-25 (a) 90∘ (b) 270∘ (c) 0 ∘ (d) 180∘ 9. Which of the following parameters is the same for all hydrogen-like atoms and ions in their ground states? (a) Radius of the orbit NCERT Page-420 / N-294 (b) Speed of the electron (c) Energy of the atom (d) Orbital angular momentum of the electron 10. An α-particle of energy 5MeV is scattered through 180∘ by a fixed uranium nucleus. The distance of closest approach is of the order of NCERT Page-420 / N-295 (a) 10−12cm (b) 10−10cm (c) 10−20cm (d) 10−15cm 11. The distance of closest approach of a certain nucleus is 7.2 fm and it has a charge of 1.28 × 10−17C. The number of neutrons inside the nucleus of an atom is NCERT Page-420 / N-295 (a) 136 (b) 142 (c) 140 (d) 132 12. If the collision between the incident α-particle whose kinetic energy is T and electric charge 2e and the nucleus were head on. The correct relation between the distance of closest approach D and T is NCERT Page-420 / N-295 (a) D ∝ 1 T (b) D ∝ T (c) D ∝ T 2 (d) D ∝ 1 T2 13. 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 Z1Z2 NCERT Page-416/ N-295 (b) inversely proportional to Z1 (c) directly proportional to mass M1 (d) directly proportional to M1 × M2 14. The diagram shows the path of four α-particles of the same energy being scattered by the nucleus of an atom simulateneously which of those is not physically possible? NCERT Page-418 / N-294
(a) 3 and 4 (b) 2 and 3 (c) 1 and 4 (d) 4 only 15. An α particle passes rapidly through the exact centre of a hydrogen molecule, moving on a line perpendicular to the internuclear axis. The distance between the nuclei is b. Where on its path does the α particle experience the greatest force? (Assume that the nuclei do not move much during the passage of the α particle. Also neglect the electric field of the electrons in the molecule.) NCERT Page-418 / N-295 (a) b 2 (b) b 2√2 (c) b √2 (d) None of these 16. An α-particle of 10MeV collides head-on with a copper nucleus (Z = 29) and is deflected back. Then, the minimum distance of approach between the centres of the two is: NCERT Page-418 / N-299 (a) 8.4 × 10−15cm (b) 8.4 × 10−15m (c) 4.2 × 10−15m (d) 4.2 × 10−15cm 17. In Rutherford's experiment, the number of α-particles scattered through an angle of 60∘ . by a silverfoil is 200 per minute. When the silver foil is replaced by a copper foil of the same thickness, the number of α-particles scattered through an angle of 60∘ per minute is: NCERT Page-418 / N-295 (a) 200×ZCu ZAg (b) 200 × ( ZCu ZAg) 2 (c) 200 × ZAg ZCu (d) 200 × ( ZAg ZCu ) 2
12.3 ATOMIC SPECTRA 18. Hydrogen atom from excited state comes to the ground by emitting a photon of wavelength λ. The value of principal quantum number ' n ' of the excited state will be: NCERT Page-422 (a) √ λR λ−1 (b) √ λR λR−1 (c) √ λ λR−1 (d) √ λR2 λR−1 19. Which of the following series in the spectrum of hydrogen atom lies in the visible region of the electromagnetic spectrum? NCERT Page-421 (a) Paschen series (c) Lyman series (b) Balmer series (d) Brackett series 20. The Balmer series for the H-atom can be observed NCERT Page-422 (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 21. The largest wavelength in the ultraviolet region of the hydrogen spectrum is 122nm. The smallest wavelength in the infrared region of the hydrogen spectrum (to the nearest integer) is NCERT Page-422 (a) 802nm (b) 823nm (c) 1882nm (d) 1648nm 22. 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 NCERT Page-422 (a) 656.3nm, n = 3 (b) 486.1nm, n = 4 (c) 410.2nm, n = 5 (d) 364.6nm, n = ∞ 23. The first line of Balmer series has wavelength 6563Å. What will be the wavelength of the first member of Lyman series NCERT Page-422 (a) 1215.4Å (b) 2500Å (c) 7500Å (d) 600Å 24. Taking Rydberg's constant RH = 1.097 × 107m, first and second wavelength of Balmer series in hydrogen spectrum is NCERT Page-422 (a) 2000Å, 3000Å (b) 1575Å, 2960Å