- According to Bohr’s model, what determines the stability of an electron’s orbit?
A) Distance from the nucleus.
B) Energy of the electron.
C) Angular momentum.
D) All of the above.
Answer: D) All of the above.
Explanation: The stability of an electron’s orbit is influenced by its distance from the nucleus, energy, and angular momentum.
- Which of the following correctly defines the energy level of an electron in a hydrogen atom?
A) E = -13.6/n² eV
B) E = 13.6/n² eV
C) E = -n²/13.6 eV
D) E = n²/13.6 eV
Answer: A) E = -13.6/n² eV.
Explanation: This formula shows that energy levels in hydrogen are quantized and negative, indicating a bound state.
- Which series of spectral lines occurs when electrons fall to the first energy level (n=1) in hydrogen?
A) Balmer series
B) Lyman series
C) Paschen series
D) Brackett series
Answer: B) Lyman series.
Explanation: The Lyman series corresponds to transitions to the ground state (n=1) and is in the ultraviolet region of the spectrum.
- What is the shape of the electron orbits in the Bohr model?
A) Elliptical
B) Circular
C) Spherical
D) Irregular
Answer: B) Circular.
Explanation: Bohr modeled the electron orbits as circular paths around the nucleus.
- Which of the following describes a key limitation of the Bohr model?
A) It can explain multi-electron systems accurately.
B) It doesn’t account for electron wave behavior.
C) It explains the photoelectric effect.
D) It applies to all elements equally.
Answer: B) It doesn’t account for electron wave behavior.
Explanation: The Bohr model does not incorporate the wave nature of electrons, which is essential in modern quantum mechanics.
- In the Bohr model, the quantization of energy levels is derived from which principle?
A) Conservation of energy
B) Wave-particle duality
C) Angular momentum quantization
D) Heisenberg uncertainty principle
Answer: C) Angular momentum quantization.
Explanation: The quantization of energy levels in the Bohr model arises from the requirement that the angular momentum of the electron is quantized.
- Which equation represents the relationship between energy and wavelength of emitted light?
A) E = mc²
B) E = hv
C) E = 1/2 mv²
D) E = Fd
Answer: B) E = hv.
Explanation: This equation relates energy (E) to frequency (v) using Planck’s constant (h).
- When an electron in a hydrogen atom falls from n=3 to n=2, what type of photon is emitted?
A) Gamma ray
B) X-ray
C) Visible light
D) Radio wave
Answer: C) Visible light.
Explanation: The transition from n=3 to n=2 typically corresponds to visible light emissions within the Balmer series.
- Which statement best describes the nature of electron orbits in the Bohr model?
A) They are random.
B) They are fixed paths with no variability.
C) They are influenced by external magnetic fields.
D) They can change size based on temperature.
Answer: B) They are fixed paths with no variability.
Explanation: In the Bohr model, electron orbits are defined and fixed, with quantized energy levels.
- The concept of an “excited state” in an atom refers to what?
A) The electron is in its ground state.
B) The electron has absorbed energy and moved to a higher energy level.
C) The atom is ionized.
D) The electron is at rest.
Answer: B) The electron has absorbed energy and moved to a higher energy level.
Explanation: An excited state occurs when an electron gains energy and moves to a higher orbit.
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