Chapter Exam

Chapter-12 Atoms — Online MCQ Test

Q: According to Rutherford's atomic model, where is most of the mass of an atom concentrated?

Answer: B. In the nucleus — Rutherford's model established that the nucleus contains most of the atom's mass and positive charge, while electrons orbit around it.

Q: In Bohr's model of the hydrogen atom, what does the principal quantum number (n) represent?

Answer: C. The energy level or shell of the electron — The principal quantum number n identifies the electron's energy level, with n = 1 being the ground state, n = 2 the first excited state, and so on.

Q: If an electron in a hydrogen atom transitions from n=3 to n=1, what type of radiation is emitted?

Answer: C. Ultraviolet radiation — The energy difference between n=3 and n=1 is large enough (approximately 12.1 eV) to produce ultraviolet radiation.

Q: The number of possible transitions from n=4 to lower levels in a hydrogen atom is:

Answer: C. 6 — From n=4, electrons can transition to n=3, n=2, or n=1 (3 direct transitions). From n=3 (after reaching it), transitions to n=2 or n=1 (2 more). From n=2 to n=1 (1 more). Total = 3+2+1 = 6 transitions.

PHYSICS · CLASS 12 SECOND PUC · Karnataka State Board

Practice Chapter-12 Atoms with a free chapter-wise online MCQ test for Karnataka State Board CLASS 12 SECOND PUC PHYSICS. This chapter covers: Rutherford model - Bohr model - alpha scattering - energy levels - hydrogen spectrum. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter-12 Atoms — Important Questions & Answers (FAQ)

Frequently asked questions from Karnataka State Board CLASS 12 SECOND PUC PHYSICS — Chapter-12 Atoms, with answers and explanations. These are sample questions; the exam has its own separate question set.

According to Rutherford's atomic model, where is most of the mass of an atom concentrated?

A. In the electron shells
B. In the nucleus ✓
C. Uniformly distributed throughout the atom
D. In the outermost electron orbit

Answer: B. In the nucleus
Rutherford's model established that the nucleus contains most of the atom's mass and positive charge, while electrons orbit around it.

In Bohr's model of the hydrogen atom, what does the principal quantum number (n) represent?

A. The charge of the nucleus
B. The angular momentum of the electron
C. The energy level or shell of the electron ✓
D. The radius of the nucleus

Answer: C. The energy level or shell of the electron
The principal quantum number n identifies the electron's energy level, with n = 1 being the ground state, n = 2 the first excited state, and so on.

If an electron in a hydrogen atom transitions from n=3 to n=1, what type of radiation is emitted?

A. Infrared radiation
B. Visible light
C. Ultraviolet radiation ✓
D. X-rays

Answer: C. Ultraviolet radiation
The energy difference between n=3 and n=1 is large enough (approximately 12.1 eV) to produce ultraviolet radiation.

The number of possible transitions from n=4 to lower levels in a hydrogen atom is:

A. 3
B. 4
C. 6 ✓
D. 10

Answer: C. 6
From n=4, electrons can transition to n=3, n=2, or n=1 (3 direct transitions). From n=3 (after reaching it), transitions to n=2 or n=1 (2 more). From n=2 to n=1 (1 more). Total = 3+2+1 = 6 transitions.

Which statement about the Bohr model is TRUE?

A. It successfully explains the spectra of all atoms, including helium
B. It is based on quantum mechanics principles
C. It correctly predicts the hydrogen spectrum and explains quantization of energy levels ✓
D. It accounts for the fine structure of spectral lines

Answer: C. It correctly predicts the hydrogen spectrum and explains quantization of energy levels
While limited to hydrogen-like atoms, Bohr's model successfully explained the hydrogen spectrum and introduced the concept of quantized energy levels, a major advance in atomic physics.