Q1. Which sub-atomic particle was discovered by J.J. Thomson?
a) Proton
b) Neutron
c) Electron
d) Positron
Answer: c) Electron
Explanation: J.J. Thomson discovered the electron in 1897. His experiments with cathode rays led to the identification of the electron as a fundamental sub-atomic particle carrying a negative charge.
Q2. What was the main conclusion of Rutherford’s gold foil experiment?
a) Atoms are mostly empty space
b) Electrons orbit the nucleus in fixed paths
c) Atoms are indivisible
d) Neutrons form the nucleus of an atom
Answer: a) Atoms are mostly empty space
Explanation: Rutherford’s gold foil experiment showed that most of the alpha particles passed straight through the foil, suggesting that atoms are mostly empty space, with a small, dense, positively charged nucleus.
Q3. According to Bohr’s atomic model, how do electrons behave in an atom?
a) Electrons move randomly around the nucleus
b) Electrons revolve in fixed orbits with specific energies
c) Electrons are stationary
d) Electrons are embedded in a positively charged sphere
Answer: b) Electrons revolve in fixed orbits with specific energies
Explanation: Bohr’s model postulated that electrons revolve around the nucleus in fixed orbits, or shells, and each orbit has a specific energy level.
Q4. What is the maximum number of electrons that can be accommodated in the M-shell?
a) 2
b) 8
c) 18
d) 32
Answer: c) 18
Explanation: According to the formula 2n^2 for calculating the maximum number of electrons in a shell (where n is the shell number), the M-shell (n=3) can hold a maximum of 2(3)^2 = 18 electrons.
Q5. Which statement correctly defines isotopes?
a) Atoms with the same number of protons but different numbers of electrons
b) Atoms with different numbers of protons but the same number of neutrons
c) Atoms with the same number of protons but different numbers of neutrons
d) Atoms with the same number of electrons but different numbers of protons
Answer: c) Atoms with the same number of protons but different numbers of neutrons
Explanation: Isotopes are atoms of the same element (having the same number of protons) that differ in the number of neutrons, leading to different mass numbers.
Q6. What is the valency of an element with a completely filled outermost shell?
a) 1
b) 2
c) 0
d) 8
Answer: c) 0
Explanation: Elements with a completely filled outermost shell are stable and show little chemical activity, hence their valency, which is a measure of an atom’s combining power, is zero.
Q7. How did the discovery of the electron and proton lead to the failure of one aspect of Dalton’s atomic theory?
a) It proved that atoms could be transformed into other elements
b) It showed that atoms are not the smallest particles
c) It indicated that atoms are divisible into smaller sub-atomic particles
d) It demonstrated the existence of isotopes
Answer: c) It indicated that atoms are divisible into smaller sub-atomic particles
Explanation: Dalton’s atomic theory posited that atoms were indivisible and indestructible. The discovery of electrons and protons, smaller sub-atomic particles within the atom, contradicted this aspect of the theory.
Q8. Which experiment led to the conclusion that the nucleus is very small compared to the size of the atom?
a) Thomson’s cathode ray experiment
b) Rutherford’s gold foil experiment
c) Bohr’s hydrogen spectrum analysis
d) Chadwick’s neutron discovery
Answer: b) Rutherford’s gold foil experiment
Explanation: Rutherford’s gold foil experiment revealed that the nucleus is very small compared to the atom’s size. This conclusion was drawn from the observation that most alpha particles passed through the gold foil without deflection.
Q9. What is the charge of a neutron?
a) Positive
b) Negative
c) Neutral
d) Variable
Answer: c) Neutral
Explanation: The neutron is a sub-atomic particle found in the nucleus of an atom. It has no electric charge, hence it is neutral.
Q10. In the context of Rutherford’s model of an atom, what was unexpected about the alpha particles’ scattering?
a) They passed straight through the gold foil
b) They were deflected at small angles
c) They were absorbed by the foil
d) Some were deflected back nearly 180 degrees
Answer: d) Some were deflected back nearly 180 degrees
Explanation: Rutherford’s experiment led to the surprising observation that a few alpha particles rebounded almost directly back, indicating the presence of a dense, positively charged nucleus.
Q11. Which of the following is not a feature of Bohr’s model of the atom?
a) Electrons revolve in discrete orbits
b) Electrons radiate energy as they revolve
c) Electrons in a particular orbit have fixed energy
d) The model assumes the existence of a nucleus
Answer: b) Electrons radiate energy as they revolve
Explanation: Contrary to this statement, Bohr’s model proposed that electrons in discrete orbits do not radiate energy. The radiation of energy occurs only when an electron jumps from one orbit to another.
Q12. Which element has an atomic number of 6?
a) Hydrogen
b) Helium
c) Carbon
d) Oxygen
Answer: c) Carbon
Explanation: Carbon has an atomic number of 6, which means it has 6 protons in its nucleus.
Q13. What is the valency of an element with one electron in its outermost shell?
a) 0
b) 1
c) 7
d) 8
Answer: b) 1
Explanation: Elements with one electron in their outermost shell tend to lose that electron to achieve a stable electronic configuration, giving them a valency of 1.
Q14. According to the Bohr-Bury scheme, what is the maximum number of electrons that can be accommodated in the outermost shell?
a) 2
b) 8
c) 18
d) 32
Answer: b) 8
Explanation: The Bohr-Bury scheme states that the maximum number of electrons that can be accommodated in the outermost shell of an atom is 8.
Q15. The discovery of which particle by J. Chadwick explained the discrepancy in atomic mass?
a) Electron
b) Proton
c) Neutron
d) Positron
Answer: c) Neutron
Explanation: J. Chadwick’s discovery of the neutron in 1932 explained why atoms had more mass than could be accounted for by protons and electrons alone.
Q16. What determines the atomic number of an element?
a) Number of electrons
b) Number of protons
c) Number of neutrons
d) Total number of nucleons
Answer: b) Number of protons
Explanation: The atomic number of an element is determined by the number of protons in the nucleus of its atoms.
Q17. Which model of the atom is described as a ‘plum pudding’ model?
a) Rutherford’s model
b) Bohr’s model
c) Thomson’s model
d) Dalton’s model
Answer: c) Thomson’s model
Explanation: J.J. Thomson’s model of the atom is often described as a ‘plum pudding’ model. It depicted the atom as a sphere of positive charge with electrons embedded in it like plums in a pudding.
Q18. What does the alpha particle scattering experiment tell us about the nucleus of an atom?
a) The nucleus is negatively charged
b) The nucleus is positively charged and very dense
c) The nucleus contains only neutrons
d) The nucleus is of negligible mass
Answer: b) The nucleus is positively charged and very dense
Explanation: Rutherford’s alpha particle scattering experiment revealed that the nucleus of an atom is positively charged and very dense, as some alpha particles were deflected at large angles.
Q19. The presence of how many electrons in the outermost shell of an atom makes it chemically inert?
a) 2 or 8
b) 1 or 7
c) 4 or 6
d) 3 or 5
Answer: a) 2 or 8
Explanation: Atoms with either 2 (in the case of helium) or 8 electrons in their outermost shell are chemically inert, as they have achieved a stable electronic configuration.
Q20. What property of an element defines its chemical behavior?
a) Atomic mass
b) Atomic number
c) Number of nucleons
d) Valency
Answer: d) Valency
Explanation: Valency, the combining capacity of an atom, primarily defines its chemical behavior. It determines how an element will combine with other elements.
Q21. Which sub-atomic particle was discovered by E. Goldstein?
a) Electron
b) Proton
c) Neutron
d) Positron
Answer: b) Proton
Explanation: E. Goldstein is credited with the discovery of the proton. He observed positively charged particles in a gas discharge experiment, which were later identified as protons.
Q22. What is the maximum number of electrons that can be accommodated in the L-shell (second orbit)?
a) 2
b) 8
c) 18
d) 32
Answer: b) 8
Explanation: According to the formula 2n², where n is the orbit number, the L-shell (n=2) can hold a maximum of 2(2)² = 8 electrons.
Q23. In the context of atomic number and mass number, what does the symbol 
represent?
a) Carbon with 6 neutrons and 6 protons
b) Carbon with 12 protons and 6 neutrons
c) Carbon with 6 protons and 6 electrons
d) Carbon with 6 protons and a mass number of 12
Answer: d) Carbon with 6 protons and a mass number of 12
Explanation: In the symbol , 6 represents the atomic number (protons) and 12 represents the mass number (protons + neutrons). This indicates carbon with 6 protons and a mass number of 12.
Q24. Which of the following is a characteristic of isotopes?
a) Same atomic number, different mass numbers
b) Different atomic numbers, same mass numbers
c) Same number of electrons, different number of protons
d) Same chemical properties, different physical properties
Answer: a) Same atomic number, different mass numbers
Explanation: Isotopes of an element have the same atomic number (same number of protons) but different mass numbers due to a different number of neutrons. They often exhibit the same chemical properties but can have different physical properties.
Q25. What is an isobar?
a) Atoms with the same number of protons but different numbers of neutrons
b) Atoms with different atomic numbers but the same mass number
c) Atoms with the same atomic number but different mass numbers
d) Atoms with the same number of neutrons but different numbers of protons
Answer: b) Atoms with different atomic numbers but the same mass number
Explanation: Isobars are atoms of different elements (hence different atomic numbers) that have the same mass number (total number of protons and neutrons).
Q26. What experimental evidence supports the existence of neutrons in the nucleus?
a) Cathode ray experiments
b) Gold foil scattering experiment
c) Discovery of isotopes
d) Nuclear reactions and their byproducts
Answer: d) Nuclear reactions and their byproducts
Explanation: The existence of neutrons in the nucleus was supported by observing nuclear reactions and their byproducts, as neutrons do not carry a charge and were not detected through traditional charge-based experiments.
Q27. What is the significance of the quantum model in understanding the electron’s behavior in an atom?
a) It defines the exact path of an electron around the nucleus
b) It provides a probabilistic model of the electron’s position
c) It confirms that electrons orbit the nucleus in perfect circles
d) It suggests that electrons are stationary
Answer: b) It provides a probabilistic model of the electron’s position
Explanation: The quantum model of the atom introduces the concept of probability in determining the position of electrons, unlike the well-defined orbits in Bohr’s model.
Q28. Which element has an atomic number of 7?
a) Hydrogen
b) Helium
c) Nitrogen
d) Oxygen
Answer: c) Nitrogen
Explanation: Nitrogen has an atomic number of 7, meaning it has 7 protons in its nucleus.
Q29. In Bohr’s model of the atom, what happens when an electron jumps from a higher energy orbit to a lower one?
a) The electron absorbs energy
b) The electron emits energy
c) The electron becomes a neutron
d) The atomic number increases
Answer: b) The electron emits energy
Explanation: According to Bohr’s model, when an electron jumps from a higher energy orbit to a lower one, it emits energy in the form of electromagnetic radiation.
Q30. What is the total number of electrons in a sodium atom with atomic number 11?
a) 11
b) 12
c) 23
d) 22
Answer: a) 11
Explanation: The atomic number of sodium is 11, which indicates it has 11 protons and, to be electrically neutral, it must also have 11 electrons.
Q31. What does the term ‘nucleons’ refer to in an atom?
a) Only protons
b) Only neutrons
c) Both protons and neutrons
d) Protons, neutrons, and electrons
Answer: c) Both protons and neutrons
Explanation: Nucleons are the particles found in the nucleus of an atom, which include both protons and neutrons.
Q32. What is the primary difference in the physical properties of isotopes of the same element?
a) Chemical reactivity
b) Electron configuration
c) Atomic number
d) Atomic mass
Answer: d) Atomic mass
Explanation: Isotopes of the same element differ in their number of neutrons, leading to different atomic masses. This difference can affect their physical properties, like melting and boiling points, but their chemical properties remain similar due to the same electron configuration.
Q33. What was a major limitation of Rutherford’s atomic model?
a) It could not explain the stability of atoms
b) It suggested that atoms are mostly empty space
c) It identified the presence of the nucleus
d) It included negatively charged electrons
Answer: a) It could not explain the stability of atoms
Explanation: Rutherford’s model, which depicted electrons orbiting a nucleus, couldn’t explain why atoms are stable and why orbiting electrons don’t radiate energy and collapse into the nucleus.
Q34. According to the atomic theory, what is responsible for the chemical behavior of an atom?
a) Its nucleus
b) The number of protons
c) Its electron configuration
d) The size of the atom
Answer: c) Its electron configuration
Explanation: The chemical behavior of an atom is largely determined by the arrangement and number of electrons in its outermost shell, affecting how it bonds with other atoms.
Q35. What is the significance of the mass number in an atom?
a) It determines the chemical properties of the atom
b) It is the sum of the number of protons and neutrons in the nucleus
c) It equals the number of electrons in the atom
d) It indicates the atom’s position in the periodic table
Answer: b) It is the sum of the number of protons and neutrons in the nucleus
Explanation: The mass number of an atom is the total number of protons and neutrons (nucleons) in its nucleus, reflecting the atom’s mass.
Q36. Which of the following best represents the electronic configuration of an atom?
a) The distribution of electrons in different shells
b) The number of protons and neutrons in the nucleus
c) The total number of electrons and protons
d) The arrangement of atoms in a molecule
Answer: a) The distribution of electrons in different shells
Explanation: The electronic configuration of an atom describes how electrons are distributed in various energy levels or shells around the nucleus.
Q37. What defines the atomic number of an element?
a) The total number of electrons
b) The total number of protons in the nucleus
c) The sum of protons and neutrons
d) The number of neutrons in the nucleus
Answer: b) The total number of protons in the nucleus
Explanation: The atomic number of an element is defined by the number of protons in the nucleus of its atoms.
Q38. How does the discovery of isotopes contradict one aspect of Dalton’s atomic theory?
a) It shows that atoms are divisible
b) It proves that all atoms of an element do not have identical properties
c) It indicates that atoms can be transformed into other elements
d) It reveals that atoms are not the smallest particles
Answer: b) It proves that all atoms of an element do not have identical properties
Explanation: Dalton’s atomic theory stated that all atoms of a given element are identical in mass and properties. The discovery of isotopes, which are atoms of the same element with different masses, contradicted this aspect.
Q39. In Bohr’s model, what happens to an electron when it absorbs energy?
a) It moves to a lower energy orbit
b) It becomes a proton
c) It moves to a higher energy orbit
d) It leaves the atom
Answer: c) It moves to a higher energy orbit
Explanation: According to Bohr’s model, when an electron absorbs energy, it jumps to a higher energy orbit, moving away from the nucleus.
Q40. Which statement correctly describes the concept of valency?
a) It is the capacity of an atom to combine with another atom
b) It is determined by the number of neutrons in an atom
c) It represents the total number of electrons and protons in an atom
d) It is the same as the atomic number of an element
Answer: a) It is the capacity of an atom to combine with another atom
Explanation: Valency is a concept that describes the ability of an atom to combine with other atoms, which is determined by the number of electrons an atom can lose, gain, or share in a chemical reaction.
Q41. Which atomic model proposed that atoms have a dense central nucleus?
a) Dalton’s model
b) Thomson’s model
c) Rutherford’s model
d) Bohr’s model
Answer: c) Rutherford’s model
Explanation: Rutherford’s atomic model proposed the existence of a dense central nucleus, based on his gold foil experiment, where he observed that some alpha particles were deflected at large angles.
Q42. What is the primary function of neutrons in the atom’s nucleus?
a) They determine the atomic number
b) They contribute to the atom’s mass
c) They stabilize the nucleus by offsetting proton-proton repulsion
d) They are involved in chemical bonding
Answer: c) They stabilize the nucleus by offsetting proton-proton repulsion
Explanation: Neutrons play a crucial role in stabilizing the nucleus. They help offset the electrostatic repulsion between positively charged protons, thus contributing to the overall stability of the nucleus.
Q43. Which statement is true about isotopes of the same element?
a) They have different atomic numbers
b) They have different numbers of protons
c) They have the same chemical properties
d) They have different electronic configurations
Answer: c) They have the same chemical properties
Explanation: Isotopes of the same element have the same atomic number and hence the same number of electrons in similar configurations, leading to identical chemical properties. Their difference lies in the number of neutrons and thus the mass number.
Q44. In Rutherford’s gold foil experiment, what conclusion was drawn from the observation that most alpha particles passed straight through the foil?
a) The atom is a solid sphere
b) The nucleus is negatively charged
c) Atoms are mostly empty space
d) Electrons are in the nucleus
Answer: c) Atoms are mostly empty space
Explanation: Rutherford concluded that atoms are mostly empty space because most alpha particles passed straight through the gold foil without any deflection.
Q45. Which of the following elements would be expected to have the highest valency?
a) Helium with 2 electrons in its outermost shell
b) Neon with 8 electrons in its outermost shell
c) Sodium with 1 electron in its outermost shell
d) Argon with 8 electrons in its outermost shell
Answer: c) Sodium with 1 electron in its outermost shell
Explanation: Sodium, with 1 electron in its outermost shell, has a valency of 1, which is higher than helium, neon, and argon, which are inert gases with full outer shells, giving them a valency of 0.
Q46. What is the maximum capacity of electrons in the N-shell (fourth orbit) of an atom?
a) 2
b) 8
c) 18
d) 32
Answer: d) 32
Explanation: According to the formula 2n^2, where n is the orbit number, the N-shell (n=4) can hold a maximum of 2(4)^2 = 32 electrons.
Q47. Which particle discovery led to the conclusion that the atom is divisible?
a) Proton
b) Neutron
c) Electron
d) Positron
Answer: c) Electron
Explanation: The discovery of the electron by J.J. Thomson provided evidence that atoms are divisible, as it showed that atoms contain smaller particles (electrons).
Q48. What is the significance of the atomic mass unit (u)?
a) It is the mass of a single electron
b) It is the mass of one mole of a substance
c) It is a standard unit for measuring the mass of atoms and molecules
d) It represents the total number of protons and electrons in an atom
Answer: c) It is a standard unit for measuring the mass of atoms and molecules
Explanation: The atomic mass unit (u) is a standard unit used to express the mass of atoms and molecules. It is defined as one-twelfth of the mass of a carbon-12 atom.
Q49. What is the primary factor that determines the identity of an element?
a) Number of neutrons
b) Number of electrons
c) Atomic number (number of protons)
d) Mass number
Answer: c) Atomic number (number of protons)
Explanation: The identity of an element is primarily determined by its atomic number, which is the number of protons in the nucleus of its atoms.
Q50. What was the key observation in Rutherford’s gold foil experiment that led to the postulation of a small, dense nucleus?
a) Alpha particles were deflected back at large angles
b) Alpha particles passed straight through without deflection
c) Electrons were found outside the nucleus
d) The gold foil disintegrated
Answer: a) Alpha particles were deflected back at large angles
Explanation: Rutherford observed that some alpha particles were deflected back at large angles, suggesting the presence of a small, dense, positively charged nucleus.
Q51. Which of the following best describes the Bohr model of the atom?
a) Electrons are embedded in a positively charged sphere
b) Electrons revolve around the nucleus in fixed orbits with specific energies
c) The nucleus is made up of electrons and protons
d) Electrons move randomly in an electron cloud around the nucleus
Answer: b) Electrons revolve around the nucleus in fixed orbits with specific energies
Explanation: Bohr’s model of the atom proposed that electrons revolve around the nucleus in fixed orbits or shells, and each orbit has a specific energy level.
Q52. What is the main characteristic of noble gases that makes them inert?
a) They have no neutrons in their nucleus
b) Their outermost shell is filled with 8 electrons (except for helium, which has 2)
c) They contain only one electron in their outermost shell
d) They have an equal number of protons and electrons
Answer: b) Their outermost shell is filled with 8 electrons (except for helium, which has 2)
Explanation: Noble gases are inert because their outermost electron shell is fully occupied (8 electrons for most noble gases, 2 for helium), making them stable and unreactive.
Q53. What is the typical charge on a proton?
a) Positive
b) Negative
c) Neutral
d) Variable
Answer: a) Positive
Explanation: Protons are subatomic particles with a positive charge, found in the nucleus of an atom.
Q54. Which element is defined by having one proton in its nucleus?
a) Helium
b) Hydrogen
c) Lithium
d) Carbon
Answer: b) Hydrogen
Explanation: Hydrogen is defined by having one proton in its nucleus. It is the simplest and lightest element on the periodic table, with an atomic number of 1.
Q55. What is the total number of electrons in a neutral atom of magnesium, which has an atomic number of 12?
a) 6
b) 12
c) 18
d) 24
Answer: b) 12
Explanation: In a neutral atom, the number of electrons equals the number of protons. Since magnesium has an atomic number of 12, it has 12 electrons.
Q56. What is the valency of chlorine, which has 7 electrons in its outermost shell?
a) 1
b) 5
c) 7
d) 8
Answer: a) 1
Explanation: Chlorine, with 7 electrons in its outermost shell, tends to gain 1 electron to achieve a stable octet configuration. Thus, its valency is 1.
Q57. Which of the following particles is not located in the nucleus of an atom?
a) Proton
b) Neutron
c) Electron
d) Nucleon
Answer: c) Electron
Explanation: Electrons are located in orbitals around the nucleus of an atom, not in the nucleus itself. Protons and neutrons (nucleons) are the particles found in the nucleus.
Q58. Which scientist’s work led to the conclusion that the atom is mostly empty space?
a) Niels Bohr
b) J.J. Thomson
c) Ernest Rutherford
d) John Dalton
Answer: c) Ernest Rutherford
Explanation: Ernest Rutherford’s gold foil experiment led to the conclusion that atoms are mostly empty space, with a small, dense nucleus.
Q59. In Bohr’s model of the atom, what is the significance of quantum jumps?
a) They explain the stability of the nucleus
b) They are transitions of electrons between different energy levels
c) They represent the movement of neutrons
d) They indicate the creation of new elements
Answer: b) They are transitions of electrons between different energy levels
Explanation: In Bohr’s model, quantum jumps refer to the transitions of electrons between different orbits or energy levels in an atom, resulting in the emission or absorption of energy.
Q60. Which is a characteristic of isotopes of a particular element?
a) Different atomic numbers
b) Different chemical properties
c) Same number of protons
d) Different electron configurations
Answer: c) Same number of protons
Explanation: Isotopes of a particular element have the same number of protons (and thus the same atomic number) but differ in the number of neutrons, leading to different mass numbers.
Q61. What determines the chemical properties of an atom?
a) Its nucleus
b) Its neutron number
c) Its electron configuration
d) Its overall size
Answer: c) Its electron configuration
Explanation: The chemical properties of an atom are primarily determined by its electron configuration, especially the electrons in the outermost shell, which are involved in chemical bonding.
Q62. Which model of the atom is known for introducing the concept of discrete energy levels for electrons?
a) Dalton’s model
b) Thomson’s model
c) Rutherford’s model
d) Bohr’s model
Answer: d) Bohr’s model
Explanation: Bohr’s model of the atom introduced the concept of discrete energy levels (orbits) for electrons, where they can revolve without radiating energy.
Q63. What is the mass number of an isotope of carbon with 6 protons and 7 neutrons?
a) 6
b) 7
c) 13
d) 14
Answer: c) 13
Explanation: The mass number of an atom is the sum of its protons and neutrons. For this carbon isotope with 6 protons and 7 neutrons, the mass number is 6 + 7 = 13.
Q64. Which of the following is a use of isotopes in science and industry?
a) Fuel in traditional combustion engines
b) Enhancing the flavor of food
c) Tracing chemical and biological processes
d) Increasing the speed of electronic devices
Answer: c) Tracing chemical and biological processes
Explanation: Isotopes are commonly used as tracers in chemical and biological processes due to their radioactivity or distinct mass, allowing scientists to track the movement and chemical changes of substances.