Bohr's Model of an Atom - MCQ Practice Set

01. According to Bohr's model of an atom, electrons move in specific orbits called:
a) Energy orbits
b) Quantum orbits
c) Stationary states
d) Angular orbits
Answer: c) Stationary states
Explanation: Bohr proposed that electrons revolve around the nucleus only in certain selected circular paths called stationary states or orbits. These orbits are associated with definite energies and are also known as energy levels or quantum levels.

02. Which principle of Bohr's model states that only certain orbits are permitted in which angular momentum of the electron is a whole number multiple of h/2π?
a) Stationary principle
b) Quantized energy levels
c) Angular momentum quantization
d) Radiation emission principle
Answer: c) Angular momentum quantization
Explanation: Bohr's model introduced the principle of angular momentum quantization, stating that only specific orbits are allowed where the angular momentum of the electron is a whole number multiple of h/2π, where 'h' is Planck's constant.

03. Electrons in Bohr's model can only exist in certain energy levels or orbits, and each orbit has a specific energy associated with it. This concept is known as:
a) Energy conservation
b) Energy quantization
c) Stationary states
d) Angular momentum quantization
Answer: b) Energy quantization
Explanation: Bohr's model introduced the concept of energy quantization, where electrons can only exist in certain energy levels or orbits, and each orbit has a specific energy associated with it. This concept explained the discrete nature of atomic spectra.

04. Bohr's model of an atom successfully explains the observed spectra for:
a) Hydrogen atom only
b) Hydrogen and helium atoms only
c) Hydrogen atom and hydrogen-like ions
d) All atoms
Answer: c) Hydrogen atom and hydrogen-like ions
Explanation: Bohr's model effectively explained the observed spectra for hydrogen atom and hydrogen-like ions such as helium, lithium, beryllium, etc. However, it could not explain the spectral series for atoms with a large number of electrons.

05. The concept of quantized energy levels in Bohr's model implies that electrons can move between these levels by:
a) Continuous energy absorption
b) Continuous energy emission
c) Absorption or emission of discrete energy packets
d) Absorption or emission of photons
Answer: c) Absorption or emission of discrete energy packets
Explanation: In Bohr's model, electrons can move between energy levels by absorbing or emitting discrete energy packets known as photons. This concept explained the discrete nature of atomic spectra observed experimentally.


06. The limitation of Bohr's model regarding the existence of various spectral lines in the hydrogen spectrum is attributed to:
a) Failure to account for radiation emission and absorption
b) Inability to predict spectral lines for atoms with large numbers of electrons
c) Arbitrary introduction of quantization of angular momentum
d) Existence of several closely spaced energy levels for each quantum number
Answer: d) Existence of several closely spaced energy levels for each quantum number
Explanation: Bohr's model successfully explained the existence of spectral lines in the hydrogen spectrum but predicted only a series of lines. However, it failed to account for the observation of several closely spaced lines, indicating the existence of multiple energy levels for each quantum number.

07. The principle of quantization of angular momentum introduced in Bohr's model states that:
a) Electrons move in specific orbits
b) Only certain orbits are permitted for electrons
c) The angular momentum of electrons is quantized
d) Electrons can emit or absorb photons
Answer: c) The angular momentum of electrons is quantized
Explanation: Bohr's model introduced the principle of quantization of angular momentum, stating that only specific orbits are allowed where the angular momentum of electrons is quantized as a whole number multiple of h/2π.

08. Bohr's model assumes that an electron in an atom:
a) Moves in continuous circular orbits
b) Is located at a definite distance from the nucleus
c) Is associated with a fixed value of momentum
d) Moves in elliptical orbits
Answer: b) Is located at a definite distance from the nucleus
Explanation: According to Bohr's model, an electron in an atom is located at a definite distance from the nucleus and revolves around it in specific circular orbits, contrary to the continuous circular orbits assumed in classical mechanics.

09. The failure of Bohr's model to explain spectral series for atoms with a large number of electrons led to the development of:
a) Quantum mechanics
b) Wave-particle duality
c) Heisenberg uncertainty principle
d) Quantum electrodynamics
Answer: a) Quantum mechanics
Explanation: Bohr's model successfully explained the spectra for hydrogen and hydrogen-like ions but failed for atoms with more electrons. This failure contributed to the development of quantum mechanics, which provided a more comprehensive understanding of atomic structure and behavior.

10. Bohr's model arbitrarily introduced the quantization of angular momentum to explain:
a) Emission and absorption of radiation
b) Existence of spectral lines in hydrogen spectrum 
c) Movement of electrons between energy levels 
d) Stability of electron orbits
Answer: d) Stability of electron orbits
Explanation: Bohr introduced the quantization of angular momentum to stabilize electron orbits and prevent electrons from spiraling into the nucleus, providing a theoretical basis for the stability of atoms. However, the arbitrary introduction of this principle without a deeper physical explanation was a limitation of his model.

11. The angular momentum quantization in Bohr's model implies that: 
a) Electrons can occupy any orbit around the nucleus 
b) Only certain orbits are permitted for electrons 
c) Electrons move in elliptical paths 
d) Electrons emit continuous radiation
Answer: b) Only certain orbits are permitted for electrons
Explanation: According to Bohr's model, only specific orbits are allowed for electrons where the angular momentum is quantized, meaning it can only take on certain discrete values.

12. Bohr's model successfully explains the spectral lines for which of the following atoms? 
a) Helium 
b) Carbon 
c) Nitrogen 
d) Oxygen
Answer: a) Helium
Explanation: Bohr's model effectively explained the observed spectra for hydrogen atom and hydrogen-like ions, which include helium, lithium, beryllium, etc.

13. The principle of quantized energy levels in Bohr's model states that electrons: 
a) Can absorb or emit continuous energy 
b) Can occupy any energy level within an atom 
c) Can only exist in certain discrete energy levels 
d) Can move between energy levels continuously
Answer: c) Can only exist in certain discrete energy levels
Explanation: According to Bohr's model, electrons can only exist in certain discrete energy levels within an atom, and they transition between these levels by absorbing or emitting discrete energy packets.



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