Atoms is a Class 12 Physics chapter that carries about 2.9% of the Physics questions in NEET. Practise it with 42 questions covering 2 topics, each with an explanation.
Sample questions on Atoms with answers
8 questions from the practice bank, spread across the chapter's topics. The full set is in the app.
Question 1: Atomic Spectra (Balmer, Lyman Series)
Which feature of Rutherford's nuclear model could it NOT explain?
- A the presence of positive charge at the centre
- B the scattering of alpha particles at large angles
- C the stability of the atom and its line spectrum
- D the small size of the nucleus
Answer: C. the stability of the atom and its line spectrum
Why: An orbiting electron should radiate energy and spiral into the nucleus, and the model gives no discrete lines. Bohr's postulates resolved both.
Question 2: Bohr Model of Hydrogen Atom
A hydrogen atom in its ground state absorbs a photon of energy 12.1 eV. The electron is raised to the orbit with n =
- A 4
- B 2
- C 3
- D ∞
Answer: C. 3
Why: E = −13.6 + 12.1 = −1.5 eV, which is the n = 3 level.
Question 3: Atomic Spectra (Balmer, Lyman Series)
The series limit (shortest wavelength) of the Lyman series is about (R = 1.097 × 10⁷ m⁻¹):
- A 91 nm
- B 122 nm
- C 656 nm
- D 365 nm
Answer: A. 91 nm
Why: For n → ∞ to n = 1, 1/λ = R, so λ = 1/(1.097 × 10⁷) ≈ 91 nm.
Question 4: Bohr Model of Hydrogen Atom
The radius of the second Bohr orbit of hydrogen is how many times the radius of the first?
- A 1/4
- B 4
- C 2
- D 8
Answer: B. 4
Why: rₙ ∝ n², so r₂/r₁ = 4.
Question 5: Atomic Spectra (Balmer, Lyman Series)
The Balmer series in the hydrogen spectrum arises from electronic transitions to the:
- A n=1 level (ground state)
- B n=2 level
- C n=3 level
- D n=4 level
Answer: B. n=2 level
Why: The Balmer series consists of transitions from higher energy levels down to n=2, and it lies partly in the visible region.
Question 6: Bohr Model of Hydrogen Atom
In Rutherford's experiment, the number of alpha particles scattered through an angle θ is proportional to:
- A 1/sin²(θ/2)
- B cos θ
- C 1/sin⁴(θ/2)
- D sin⁴(θ/2)
Answer: C. 1/sin⁴(θ/2)
Why: This was the result found by the scattering formula, and it was confirmed by the experiment of Geiger and Marsden.
Question 7: Atomic Spectra (Balmer, Lyman Series)
A group of hydrogen atoms is excited to the n = 3 level. The number of different spectral lines they can emit is:
- A 6
- B 3
- C 1
- D 2
Answer: B. 3
Why: The transitions 3→2, 3→1 and 2→1 are possible: n(n−1)/2 = 3.
Question 8: Bohr Model of Hydrogen Atom
The total energy of an electron in the nth orbit of a hydrogen atom is:
- A always positive
- B always negative, indicating a bound state
- C zero for all n
- D independent of n
Answer: B. always negative, indicating a bound state
Why: The electron is bound to the nucleus, so its total energy En = -13.6/n² eV is negative; it approaches zero only as n → ∞ (ionization).
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