- What happens when an electron transitions from a higher orbit to a lower orbit?
A) It absorbs energy.
B) It emits energy.
C) It remains stationary.
D) It loses mass.
Answer: B) It emits energy.
Explanation: When an electron transitions to a lower energy level, it emits energy, often in the form of a photon.
- Which of the following elements can be effectively described by the Bohr model?
A) Helium
B) Carbon
C) Hydrogen
D) Sodium
Answer: C) Hydrogen.
Explanation: The Bohr model is specifically designed for hydrogen and hydrogen-like atoms, as it can accurately describe their spectral lines.
- The radius of the first orbit in Bohr’s model for hydrogen is approximately:
A) 0.0529 nm
B) 0.1 nm
C) 0.5 nm
D) 1 nm
Answer: A) 0.0529 nm.
Explanation: The radius of the first orbit (n=1) in the Bohr model is known as the Bohr radius, which is approximately 0.0529 nm.
- What is the angular momentum of an electron in the nth orbit according to Bohr’s model?
A) nh/2π
B) nh
C) h/2π
D) 2πnh
Answer: A) nh/2π.
Explanation: Bohr stated that the angular momentum of an electron in a given orbit is quantized and given by the formula L = nh/2π, where n is a positive integer.
- How does the energy of an electron change as it moves closer to the nucleus in the Bohr model?
A) Increases.
B) Decreases.
C) Remains constant.
D) Becomes negative.
Answer: B) Decreases.
Explanation: As the electron moves closer to the nucleus, its energy decreases, becoming more negative, indicating a more stable state.
- The emission spectrum of hydrogen consists of which series of lines?
A) Lyman series
B) Balmer series
C) Paschen series
D) All of the above
Answer: D) All of the above.
Explanation: The hydrogen spectrum includes several series, such as the Lyman, Balmer, and Paschen series, corresponding to different transitions between energy levels.
- Which of the following best describes the concept of “excitation” in the context of the Bohr model?
A) Electron ejection from an atom.
B) Movement of an electron to a higher energy level.
C) Photon emission.
D) Orbital decay.
Answer: B) Movement of an electron to a higher energy level.
Explanation: Excitation refers to the process of an electron absorbing energy and moving to a higher energy level.
- In the Bohr model, which of the following particles is considered to be at the center of the atom?
A) Electron
B) Proton
C) Neutron
D) Nucleus
Answer: D) Nucleus.
Explanation: The nucleus, which contains protons and neutrons, is at the center of the atom, while electrons orbit around it.
- The principal quantum number (n) in the Bohr model indicates what?
A) The shape of the orbital.
B) The size and energy level of the electron orbit.
C) The orientation of the orbital.
D) The spin of the electron.
Answer: B) The size and energy level of the electron orbit.
Explanation: The principal quantum number n defines the energy level and relative size of the orbitals in which the electron resides.
- What happens to the wavelength of light emitted as an electron transitions from a higher to a lower energy state?
A) It increases.
B) It decreases.
C) It remains the same.
D) It becomes zero.
Answer: B) It decreases.
Explanation: As the energy difference between the two states increases, the wavelength of the emitted light decreases according to the energy-wavelength relationship (E = hc/λ).
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