1. Who discovered the electron?
a) J.J. Thomson
b) Rutherford
c) Bohr
d) Dalton
Answer: a) J.J. Thomson
Explanation: J.J. Thomson discovered the electron in 1897 through his experiments with cathode rays.
2. Which experiment led to the discovery of the nucleus?
a) Cathode ray experiment
b) Oil drop experiment
c) Gold foil experiment
d) Alpha particle scattering experiment
Answer: d) Alpha particle scattering experiment
Explanation: Rutherford’s alpha particle scattering experiment led to the discovery of the atomic nucleus.
3.Which of the following models of the atom was proposed by J.J. Thomson?
a) Plum pudding model
b) Nuclear model
c) Planetary model
d) Quantum model
Answer: a) Plum pudding model
Explanation: J.J. Thomson proposed the plum pudding model, where electrons were embedded in a positively charged sphere.
4. The atomic number of an element is defined as:a) Number of protons
b) Number of neutrons
c) Number of electrons
d) Sum of protons and neutrons
Answer: a) Number of protons
Explanation: The atomic number is equal to the number of protons in an atom’s nucleus.
5. The mass number of an atom is the sum of:
a) Protons and electrons
b) Neutrons and electrons
c) Protons and neutrons
d) Electrons and positrons
Answer: c) Protons and neutrons
Explanation: The mass number is the sum of protons and neutrons in an atom.
6. Which of the following is not a postulate of Dalton’s atomic theory?
a) Atoms are indivisible
b) Atoms of the same element are identical
c) Atoms can be created or destroyed in chemical reactions
d) Atoms combine in simple whole-number ratios
Answer: c) Atoms can be created or destroyed in chemical reactions
Explanation: Dalton’s atomic theory stated that atoms cannot be created or destroyed in chemical reactions.
7. What is the charge of a proton?
a) +1
b) -1
c) 0
d) +2
Answer: a) +1
Explanation: A proton carries a positive charge of +1.
8. Which particle has no charge?
a) Electron
b) Proton
c) Neutron
d) Positron
Answer: c) Neutron
Explanation: Neutrons are neutral particles, having no charge.
9. The relative mass of an electron is approximately:
a) 1 amu
b) 1/1836 of a proton
c) 0 amu
d) 1836 amu
Answer: b) 1/1836 of a proton
Explanation: The mass of an electron is about 1/1836 times that of a proton.
10. Which of the following is an isotope of hydrogen?
a) Deuterium
b) Helium
c) Oxygen
d) Nitrogen
Answer: a) Deuterium
Explanation: Deuterium is an isotope of hydrogen with one proton and one neutron.
11. Which scientist proposed the planetary model of the atom?
a) J.J. Thomson
b) Rutherford
c) Bohr
d) Schrödinger
Answer: b) Rutherford
Explanation: Rutherford proposed the planetary model where electrons orbit around a central nucleus.
12. Bohr’s model of the atom was based on which assumption?
a) Electrons move in circular orbits
b) Electrons have wave properties
c) Energy levels are continuous
d) Atoms are indivisible
Answer: a) Electrons move in circular orbits
Explanation: Bohr assumed that electrons move in fixed circular orbits around the nucleus.
13. Which of the following is a postulate of Bohr’s model?
a) Energy of electrons is quantized
b) Electrons emit radiation while in orbit
c) Electrons move in elliptical orbits
d) Electrons have no mass
Answer: a) Energy of electrons is quantized
Explanation: Bohr’s model postulated that the energy of electrons is quantized and they can only occupy certain energy levels.
14. What is the maximum number of electrons that can be accommodated in an orbit?
a) 2n
b) 2n²
c) n²
d) 4n²
Answer: b) 2n²
Explanation: According to Bohr, the maximum number of electrons in an orbit is given by 2n², where n is the orbit number
15. Which quantum number determines the shape of an orbital?
a) Principal quantum number (n)
b) Azimuthal quantum number (l)
c) Magnetic quantum number (m)
d) Spin quantum number (s)
Answer: b) Azimuthal quantum number (l)
Explanation: The azimuthal quantum number (l) determines the shape of an orbital.
16. The value of the spin quantum number (s) for an electron is:
a) +1
b) -1
c) 0
d) ±1/2
Answer: d) ±1/2
Explanation: The spin quantum number (s) can have values of +1/2 or -1/2, representing the two possible spin orientations of an electron.
17. The number of orbitals in a subshell is given by:
a) 2l + 1
b) l + 1
c) 2n²
d) n²
Answer: a) 2l + 1
Explanation: The number of orbitals in a subshell is given by 2l + 1, where l is the azimuthal quantum number.
18. Which of the following has the highest ionization energy?
a) Hydrogen
b) Helium
c) Lithium
d) Beryllium
Answer: b) Helium
Explanation: Helium has the highest ionization energy due to its small size and high effective nuclear charge.
19. What is the shape of an s-orbital?
a) Spherical
b) Dumbbell-shaped
c) Double dumbbell
d) Planar
Answer: a) Spherical
Explanation: The s-orbital is spherical in shape.
20. Which quantum number is responsible for the orientation of an orbital in space?
a) Principal quantum number (n)
b) Azimuthal quantum number (l)
c) Magnetic quantum number (m)
d) Spin quantum number (s)
Answer: c) Magnetic quantum number (m)
Explanation: The magnetic quantum number (m) determines the orientation of an orbital in space
21. What is the principal quantum number of the first energy level?
a) 1
b) 2
c) 3
d) 0
Answer: a) 1
Explanation: The principal quantum number (n) for the first energy level is 1.
22. Which of the following subshells does not exist?
a) 2s
b) 3p
c) 3f
d) 4d
Answer: c) 3f
Explanation: The f subshell starts from the fourth energy level; hence, 3f does not exist.
23. How many electrons can occupy the 3rd energy level (n=3)?
a) 2
b) 8
c) 18
d) 32
Answer: c) 18
Explanation: The maximum number of electrons in the 3rd energy level is given by 2n² = 18.
24. Which of the following is the correct order of energy levels in an atom?
a) 1s < 2s < 2p < 3s < 3p
b) 1s < 2s < 3s < 2p < 3p
c) 1s < 2p < 2s < 3p < 3s
d) 2p < 1s < 3s < 2s < 3p
Answer: a) 1s < 2s < 2p < 3s < 3p
Explanation: The correct order is based on increasing energy levels, with 2p having slightly more energy than 2s, and so on.
25. Which of the following elements has the electronic configuration [Ne] 3s²3p¹?
a) Magnesium
b) Aluminium
c) Silicon
d) Phosphorus
Answer: b) Aluminium
Explanation: Aluminium has the electronic configuration [Ne] 3s²3p¹.
26. What is the angular momentum of an electron in the first orbit of a hydrogen atom?
a) h/2π
b) 2h/π
c) h/π
d) h
Answer: a) h/2π
Explanation: According to Bohr’s model, the angular momentum of an electron in the first orbit is given by mvr = n(h/2π),
27. What is the wavelength of a photon emitted when an electron in a hydrogen atom drops from n=3 to n=2?
a) 121.6 nm
b) 102.6 nm
c) 656.3 nm
d) 486.1 nm
Answer: d) 656.3 nm
Explanation: The transition from n=3 to n=2 corresponds to the emission of light in the visible region (Hα line) with a wavelength of 656.3 nm.
28. Which of the following series of the hydrogen spectrum lies in the visible region?
a) Lyman series
b) Balmer series
c) Paschen series
d) Brackett series
Answer: b) Balmer series
Explanation: The Balmer series lies in the visible region of the electromagnetic spectrum.
29. The uncertainty principle was proposed by:
a) Bohr
b) Heisenberg
c) Einstein
d) Schrödinger
Answer: b) Heisenberg
Explanation: Heisenberg proposed the uncertainty principle, which states that it is impossible to simultaneously determine the exact position and momentum of a particle.
30. According to the de Broglie hypothesis, the wavelength of a particle is inversely proportional to its:
a) Velocity
b) Energy
c) Momentum
d) Mass
Answer: c) Momentum
Explanation: According to de Broglie, wavelength (λ) is inversely proportional to the momentum (p) of a particle, given by λ = h/p.
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