30. According to Rutherford’s model, where is most of an atom’s mass located?
[RRB Technician Grade III — 20 Dec 2024, Shift 2]
(A) In the electron shells
(B) In the nucleus
(C) In the electron cloud
(D) Equally throughout the atom
Answer: (B) In the nucleus
Explanation: Nearly the entire atomic mass is concentrated in protons and neutrons packed inside the very small nucleus. Electrons occupy much more space but have negligible mass by comparison. Rutherford inferred this dense core from alpha-particle scattering observations.
29. Which physicist is famous for the gold foil experiment?
[SSC Stenographer — 11 Dec 2024, Shift 2]
(A) John Dalton
(B) J. J. Thomson
(C) Ernest Rutherford
(D) Niels Bohr
Answer: (C) Ernest Rutherford
Explanation: Ernest Rutherford interpreted the alpha-particle scattering data collected by Geiger and Marsden, showing that atoms contain compact, positively charged nuclei. The experimental results challenged Thomson’s diffuse positive-charge model and led Rutherford to propose the nuclear atomic model.
28. Which statement is INCORRECT about Rutherford’s model of an atom?
[RRB ALP CBT-I — 26 Nov 2024, Shift 2]
(A) Electrons revolve around the nucleus in circular paths.
(B) The atom has a positively charged centre called the nucleus.
(C) Electrons revolve around the nucleus in elliptical paths.
(D) The nucleus is extremely small compared with the atom.
Answer: (C) Electrons revolve around the nucleus in elliptical paths.
Explanation: The textbook Rutherford model pictured electrons revolving around a small positively charged nucleus in circular paths, not specified elliptical paths. Its serious limitation was that classically accelerated electrons should radiate energy, making the proposed atom unstable without further assumptions.
27. Ernest Rutherford used gold foil about how many atoms thick for his alpha-particle scattering experiment?
[SSC CGL Tier-I — 11 Sept 2024, Shift 3]
(A) 500 atoms
(B) 1000 atoms
(C) 900 atoms
(D) 700 atoms
Answer: (B) 1000 atoms
Explanation: Gold is extremely malleable and can be beaten into very thin foil. A sheet roughly one thousand atoms thick allowed energetic alpha particles to interact with only a thin layer, making their scattering informative about the atom’s internal charge distribution.
26. Arrange these discoveries from earliest to latest: (I) Pi meson, (II) Neutron, (III) Electron, (IV) Proton.
[UPPSC RO/ARO General Studies — 11 Feb 2024]
(A) I, III, IV, II
(B) III, II, I, IV
(C) III, IV, II, I
(D) III, IV, I, II
Answer: (C) III, IV, II, I
Explanation: J. J. Thomson identified the electron in 1897. Rutherford’s proton work followed around 1917–1919, then Chadwick discovered the neutron in 1932. The pion was identified in cosmic-ray studies in 1947. Hence the sequence is III, IV, II, I.
25. Which Group 13 element has atomic number 113 and configuration [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p¹?
[SSC CHSL Tier-I — 14 Aug 2023, Shift 1]
(A) Gallium
(B) Indium
(C) Nihonium
(D) Thallium
Answer: (C) Nihonium
Explanation: Nihonium, symbol Nh, is the synthetic element with atomic number 113. Its outer electronic arrangement ends in 7s²7p¹, consistent with Group 13. Gallium, indium and thallium are lighter members of the same group with different atomic numbers.
24. Which is the increasing order of electron affinity of the halogens?
[SSC CHSL Tier-I — 11 Aug 2023, Shift 1]
(A) F < I < Br < Cl
(B) I < Br < Cl < F
(C) I < Br < F < Cl
(D) I > Br > F < Cl
Answer: (C) I < Br < F < Cl
Explanation: For the halogens, chlorine has a greater first electron affinity than fluorine because fluorine’s compact 2p subshell produces greater electron-electron repulsion upon electron addition. Bromine and iodine show progressively lower values as atomic size and shielding increase.
23. In which year did Niels Bohr propose his quantum-based theory of the hydrogen atom?
[SSC CHSL Tier-I — 9 Aug 2023, Shift 1]
(A) 1919
(B) 1921
(C) 1909
(D) 1913
Answer: (D) 1913
Explanation: In 1913 Bohr developed a model that allowed electrons to occupy only specific stationary energy states. An electron could emit or absorb light by transitioning between them. This idea successfully accounted for regularities in the hydrogen spectrum.
22. Which set of quantum numbers can describe an electron in a 4f orbital?
[SSC CHSL Tier-I — 3 Aug 2023, Shift 1]
(A) n = 4, l = 3, m = +1, s = +½
(B) n = 3, l = 2, m = −2, s = +½
(C) n = 4, l = 4, m = −4, s = −½
(D) n = 4, l = 3, m = +4, s = +½
Answer: (A) n = 4, l = 3, m = +1, s = +½
Explanation: For a 4f electron the principal quantum number must be 4 and the orbital angular momentum quantum number must be l = 3. The magnetic quantum number may range from −3 to +3, and spin is ±½.
21. Whose work in 1808 provided a physical picture of compounds forming by combinations of different types of atoms?
[SSC CGL Tier-I — 26 Jul 2023, Shift 1]
(A) George Zweig
(B) J. J. Thomson
(C) Niels Bohr
(D) John Dalton
Answer: (D) John Dalton
Explanation: John Dalton’s atomic theory described matter as made of atoms and compounds as fixed combinations of atoms of different elements. His work helped connect the laws of chemical combination to a particle model, though later discoveries modified some of his assumptions.
