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1. The negatively charged subatomic particle present in an atom is called the:
A. Electron
B. Proton
C. Neutron
D. Positron
Answer: A. Electron
Explanation: The electron is a fundamental subatomic particle carrying a negative electric charge, discovered by J.J. Thomson.
2. The positively charged subatomic particle present in the nucleus of an atom is called the:
A. Proton
B. Electron
C. Neutron
D. Photon
Answer: A. Proton
Explanation: The proton is a positively charged particle found within the atomic nucleus, discovered through experiments by Rutherford and others.
3. The subatomic particle with no electric charge, found in the nucleus, is called the:
A. Neutron
B. Electron
C. Proton
D. Positron
Answer: A. Neutron
Explanation: The neutron, discovered by James Chadwick, is electrically neutral and resides alongside protons in the nucleus.
4. Who discovered the electron through experiments with cathode ray tubes?
A. J.J. Thomson
B. Ernest Rutherford
C. James Chadwick
D. Niels Bohr
Answer: A. J.J. Thomson
Explanation: J.J. Thomson is credited with discovering the electron in 1897 through his experiments involving cathode rays.
5. Rutherford's gold foil experiment led to the discovery of the:
A. Atomic nucleus
B. Electron
C. Neutron
D. Proton exclusively
Answer: A. Atomic nucleus
Explanation: Rutherford's alpha particle scattering experiment revealed the existence of a small, dense, positively charged nucleus at the centre of the atom.
6. According to Rutherford's atomic model, most of the mass and positive charge of an atom is concentrated in its:
A. Nucleus
B. Electron cloud
C. Outer shell
D. Orbitals
Answer: A. Nucleus
Explanation: Rutherford's model proposed that nearly all the atom's mass and positive charge reside in a tiny, dense central nucleus.
7. Bohr's model of the atom proposed that electrons revolve around the nucleus in fixed circular paths called:
A. Orbits or shells
B. Orbitals only
C. Subshells only
D. Quantum clouds
Answer: A. Orbits or shells
Explanation: Bohr proposed that electrons move in specific, quantised circular orbits or shells around the nucleus, each with a fixed energy.
8. According to Bohr's model, an electron does not radiate energy while moving in a:
A. Stationary (fixed) orbit
B. Random path
C. Elliptical path only
D. Nucleus itself
Answer: A. Stationary (fixed) orbit
Explanation: Bohr postulated that electrons in specific stationary orbits do not lose energy, contrary to classical electromagnetic theory.
9. The atomic number of an element represents the number of:
A. Protons in the nucleus
B. Neutrons in the nucleus
C. Electrons in the outermost shell only
D. Total nucleons
Answer: A. Protons in the nucleus
Explanation: Atomic number (Z) is defined as the number of protons present in the nucleus of an atom, uniquely identifying the element.
10. The mass number of an atom is the sum of the number of:
A. Protons and neutrons
B. Protons and electrons
C. Neutrons and electrons
D. Only neutrons
Answer: A. Protons and neutrons
Explanation: Mass number (A) represents the total count of protons and neutrons present in the nucleus of an atom.
11. Atoms of the same element having the same atomic number but different mass numbers are called:
A. Isotopes
B. Isobars
C. Isotones
D. Isoelectronic species
Answer: A. Isotopes
Explanation: Isotopes are variants of the same element with an identical number of protons but differing numbers of neutrons.
12. According to Heisenberg's Uncertainty Principle, it is impossible to simultaneously determine the exact:
A. Position and momentum of a subatomic particle
B. Charge and mass of a particle
C. Colour and shape of an atom
D. Number of protons and neutrons
Answer: A. Position and momentum of a subatomic particle
Explanation: This principle states a fundamental limit on the precision with which both the position and momentum of a particle can be known simultaneously.
13. The branch of physics dealing with the wave-particle duality and behaviour of electrons is called:
A. Quantum mechanics
B. Classical mechanics
C. Thermodynamics
D. Electrodynamics only
Answer: A. Quantum mechanics
Explanation: Quantum mechanics provides the theoretical framework for understanding the dual wave-particle nature of electrons and their behaviour in atoms.
14. The region around the nucleus where the probability of finding an electron is maximum is called an:
A. Orbital
B. Orbit
C. Shell only
D. Nucleus
Answer: A. Orbital
Explanation: An orbital is defined as a three-dimensional region of space around the nucleus where an electron is most likely to be found.
15. The principal quantum number (n) determines the:
A. Size and energy of the electron shell
B. Shape of the orbital only
C. Spin of the electron only
D. Orientation of the orbital only
Answer: A. Size and energy of the electron shell
Explanation: The principal quantum number primarily determines the overall size and energy level of an electron's shell within the atom.
16. The azimuthal quantum number (l) determines the:
A. Shape of the orbital
B. Size of the shell only
C. Spin of the electron
D. Total number of electrons
Answer: A. Shape of the orbital
Explanation: The azimuthal (angular momentum) quantum number specifies the shape of the electron's orbital, such as s, p, d or f.
17. The magnetic quantum number (ml) determines the:
A. Orientation of the orbital in space
B. Shape of the orbital only
C. Spin direction of the electron
D. Overall energy of the shell
Answer: A. Orientation of the orbital in space
Explanation: The magnetic quantum number specifies the spatial orientation of a given orbital relative to a magnetic field.
18. The spin quantum number (ms) describes the:
A. Intrinsic spin direction of an electron
B. Shape of the orbital
C. Size of the orbital
D. Number of orbitals in a subshell
Answer: A. Intrinsic spin direction of an electron
Explanation: The spin quantum number indicates the intrinsic angular momentum (spin) direction of an electron, either +1/2 or -1/2.
19. Pauli's Exclusion Principle states that no two electrons in an atom can have the:
A. Same set of all four quantum numbers
B. Same principal quantum number only
C. Same charge
D. Same mass
Answer: A. Same set of all four quantum numbers
Explanation: This principle asserts that every electron within an atom must have a unique combination of all four quantum numbers.
20. According to Hund's Rule, electrons occupy degenerate orbitals singly before:
A. Pairing up within the same orbital
B. Moving to a different shell
C. Losing their charge
D. Combining with protons
Answer: A. Pairing up within the same orbital
Explanation: Hund's Rule states that electrons fill orbitals of equal energy individually first, minimizing electron-electron repulsion, before any pairing occurs.
21. The Aufbau Principle states that electrons are filled into orbitals in order of:
A. Increasing energy
B. Decreasing energy
C. Random order
D. Alphabetical order
Answer: A. Increasing energy
Explanation: The Aufbau Principle dictates that electrons occupy the lowest available energy orbitals first before filling higher energy ones.
22. The maximum number of electrons that can be accommodated in a shell with principal quantum number 'n' is given by:
A. 2n²
B. n²
C. 2n
D. n
Answer: A. 2n²
Explanation: The formula 2n² determines the maximum electron capacity of a given principal energy shell.
23. The de Broglie hypothesis proposed that particles such as electrons exhibit:
A. Wave-like properties
B. Only particle properties
C. No measurable properties
D. Only magnetic properties
Answer: A. Wave-like properties
Explanation: De Broglie proposed that moving particles, including electrons, possess an associated wavelength, exhibiting dual wave-particle behaviour.
24. The electromagnetic radiation emitted or absorbed when an electron transitions between energy levels forms a:
A. Spectrum
B. Solid
C. Nucleus
D. Compound
Answer: A. Spectrum
Explanation: Electron transitions between different energy levels result in the emission or absorption of specific wavelengths of light, forming a spectrum.
25. The lowest energy state of an atom is called its:
A. Ground state
B. Excited state
C. Ionised state
D. Transition state
Answer: A. Ground state
Explanation: The ground state refers to the atom's most stable configuration, where electrons occupy the lowest possible energy levels.
26. When an electron absorbs energy and moves to a higher energy level, the atom is said to be in an:
A. Excited state
B. Ground state
C. Neutral state
D. Stable state only
Answer: A. Excited state
Explanation: An excited state occurs when an electron gains energy and temporarily moves to a higher, less stable energy level.
27. The value of Planck's constant (h) is approximately:
A. 6.626 × 10⁻³⁴ J s
B. 3 × 10⁸ m/s
C. 9.1 × 10⁻³¹ kg
D. 1.6 × 10⁻¹⁹ C
Answer: A. 6.626 × 10⁻³⁴ J s
Explanation: Planck's constant, a fundamental constant in quantum theory, has an approximate value of 6.626 × 10⁻³⁴ joule-seconds.
28. An atom or ion is said to be isoelectronic with another species if they have the same number of:
A. Electrons
B. Protons
C. Neutrons
D. Nucleons
Answer: A. Electrons
Explanation: Isoelectronic species share an identical number of electrons, even though their atomic or ionic identities may differ.
29. The wave nature of electrons is experimentally supported by the phenomenon of:
A. Electron diffraction
B. Radioactive decay
C. Nuclear fission
D. Photoelectric emission only
Answer: A. Electron diffraction
Explanation: Electron diffraction experiments demonstrated that electrons, like light, can produce interference patterns, confirming their wave-like nature.
30. The number of orbitals present in a p subshell is:
A. Three
B. One
C. Five
D. Seven
Answer: A. Three
Explanation: The p subshell consists of three distinct orbitals (px, py, pz), each capable of holding up to two electrons.
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