83 free MCQs on Atoms, each with its own worked answer and explanation. Thomson's plum-pudding model, Rutherford's nuclear model from alpha-scattering, Bohr's postulates and hydrogen spectrum, spectral series (Lyman to Pfund), Rydberg formula, and limitations of each model.
Take the timed Atoms chapterwise test →83 practice questions on Atoms, sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Atoms notes.
The Geiger–Marsden alpha-scattering result: a few alpha particles bounce back at large angles, which rules out Thomson’s diffuse model and demands a tiny, massive, positively charged nucleus. Image: Kurzon, CC BY 3.0, via Wikimedia Commons.
Q1.
In Rutherford scattering, an alpha particle directed almost head-on toward the nucleus experiences its largest deflection because:
Q2.
For an electron in the nth Bohr orbit of hydrogen, how does its orbital period T vary with n?
Q3.
What minimum energy must a hydrogen atom in its ground state absorb to reach the n = 2 state?
Q4.
In the Bohr model, which quantity of the electron remains fixed for a particular stationary orbit?
Q5.
A hydrogen atom in the n = ∞ state represents:
Q6.
Energy of hydrogen electron in nth orbit:
Q7.
Visible light emission from hydrogen atom (Balmer series) involves transitions to:
Q8.
Rutherford's gold foil experiment showed that:
Q9.
Heisenberg's uncertainty principle states that:
Q10.
Ionization energy of hydrogen atom is:
Q11.
Lyman series of hydrogen spectrum lies in the:
Q12.
X-rays are produced when:
Q13.
The tiny, dense, positively charged core of an atom is the:
Q14.
In an atom, electrons revolve around the nucleus in:
Q15.
The model in which electrons move in fixed circular orbits was proposed by:
Q16.
Besides protons, the nucleus contains:
Q17.
The atomic number of an element equals its number of:
Q18.
Rutherford’s alpha-particle scattering experiment led to the discovery of the:
Q19.
Most of the volume of an atom is:
Q20.
The energy of an electron in an atom is:
Q21.
When an electron jumps to a lower orbit, it ___ energy:
Q22.
When an electron jumps to a higher orbit, it ___ energy:
Q23.
The lowest energy state of an atom is called the ___ state:
Q24.
The emission spectrum of hydrogen consists of discrete:
Q25.
The alpha particle used in Rutherford’s experiment is a ___ nucleus:
Q26.
A hydrogen atom in its ground state absorbs a photon of energy 12.09 eV. To which principal quantum number does the electron move?
Q27.
A hydrogen-like He<sup>+</sup> ion undergoes a transition from n = 2 to n = 1. Using R = 1.097 × 10<sup>7</sup> m<sup>-1</sup>, what is the approximate wavelength of the emitted radiation?
Q28.
The orbital period of an electron in the first Bohr orbit of hydrogen is 1.52 × 10<sup>-16</sup> s. What is its orbital period in the n = 3 orbit?
Q29.
An alpha particle of kinetic energy 5.0 MeV approaches a gold nucleus head-on. Taking Z = 79 and e<sup>2</sup>/(4πε<sub>0</sub>) = 1.44 MeV fm, what is the distance of closest approach?
Q30.
A hydrogen atom emits radiation when an electron falls from n = 4 to n = 2. What is the energy of the emitted photon?
Q31.
Photon energy for the transition n=3 to n=1 in hydrogen:
Q32.
The energy levels of hydrogen-like atoms (atomic number Z):
Q33.
The series of hydrogen spectrum in ultraviolet region is:
Q34.
Wave nature of electrons was confirmed by:
Q35.
The velocity of electron in nth orbit of hydrogen (v₁ = 2.18 × 10⁶ m/s):
Q36.
Electron in orbit has:
Q37.
In Bohr’s model, the angular momentum of an orbiting electron is quantised in units of:
Q39.
Using E<sub>n</sub> = −13.6/n² eV, the ground-state (n = 1) energy of hydrogen is:
Q40.
The energy of the n = 2 level of hydrogen is:
Q41.
As n increases, the energy levels of hydrogen become:
Q42.
The Balmer series of the hydrogen spectrum lies in the ___ region:
Q43.
The Lyman series of the hydrogen spectrum lies in the ___ region:
Q44.
The Paschen series of the hydrogen spectrum lies in the ___ region:
Q45.
The energy needed to remove the electron from the ground state of hydrogen (its ionisation energy) is:
Q46.
The radius of the first Bohr orbit of hydrogen is about:
Q47.
According to Bohr, an electron in a stationary orbit does not ___ energy:
Q48.
A spectral line’s wavelength relates to the energy difference by ΔE equals:
Q49.
In hydrogen, the transition from n = 3 to n = 2 produces a line in the ___ series:
Q50.
The number of neutrons in a nucleus equals the mass number minus the:
Q51.
A hydrogen atom in the n = 3 state is just ionised by absorbing a photon. What is the approximate wavelength of this photon? Take h = 6.6 × 10<sup>-34</sup> J s and c = 3 × 10<sup>8</sup> m s<sup>-1</sup>.
Q52.
For hydrogen, compare the photon frequencies produced by transitions n = 6 to n = 2 and n = 3 to n = 2. What is the ratio ν<sub>6→2</sub>/ν<sub>3→2</sub>?
Q53.
The de Broglie wavelength of an electron in the third Bohr orbit of hydrogen is approximately what value? Take the Bohr radius a<sub>0</sub> = 0.529 × 10<sup>-10</sup> m.
Q54.
The speed of an electron in the n = 3 orbit of He<sup>+</sup> is compared with that of an electron in the n = 2 orbit of hydrogen. What is the ratio v<sub>He+</sub>/v<sub>H</sub>?
Q55.
An electron in hydrogen is initially in the n = 2 state. It absorbs a photon of energy 2.856 eV. Which final state is reached?
Q56.
De Broglie wavelength of a thermal neutron at temperature T:
Q57.
Rydberg formula for hydrogen: 1/lambda = R(1/n<sub>1</sub>² - 1/n<sub>2</sub>²). Rydberg constant R =
Q58.
Bohr radius a₀ in terms of fundamental constants:
Q59.
Quantization of angular momentum in Bohr model arises from:
Q60.
Zeeman effect is the splitting of spectral lines in:
Q61.
The number of spectral lines when electron jumps from nth orbit to ground state:
Q62.
In Rutherford scattering, the impact parameter b for deflection by angle theta:
Q63.
Fine structure of hydrogen spectral lines arises from:
Q64.
The de Broglie wavelength of a 1 kg ball moving at 1 m/s is negligible because:
Q65.
The speed of an electron in the nth Bohr orbit is proportional to:
Q66.
The line emitted in the n = 2 to n = 1 transition of hydrogen lies in the ___ region:
Q67.
For a hydrogen-like ion of nuclear charge Z, the energy levels scale as:
Q68.
In the Rydberg formula 1/λ = R(1/n₁² − 1/n₂²), the constant R is the ___ constant:
Q69.
The kinetic energy of the electron in a hydrogen atom is ___ the magnitude of its total energy:
Q70.
The potential energy of the electron in a hydrogen atom is ___ its total energy:
Q71.
The series limit (shortest wavelength) of the Lyman series is the transition from n = ∞ to n =:
Q72.
The frequency of the radiation emitted by an atom is proportional to the ___ between the two levels:
Q73.
A key limitation of Bohr’s model is that it fails to explain the spectra of ___ atoms:
Q74.
The angular momentum of the electron in the ground state of hydrogen (n = 1) is:
Q75.
The de Broglie explanation of Bohr’s quantisation requires the orbit circumference to hold a whole number of ___ wavelengths:
Q76.
In the Bohr model of hydrogen, the radius of the n = 2 orbit (Bohr radius 0.53 Å) is:
Q77.
The energy of the electron in the n = 2 level of hydrogen (E₁ = −13.6 eV) is:
Q78.
The number of distinct spectral lines emitted when hydrogen atoms de-excite from the n = 4 level is:
Q79.
The angular momentum of an electron in the n = 3 orbit of hydrogen is:
Q80.
In the Bohr model, the speed of the electron is inversely proportional to n. In the n = 2 orbit the speed is:
Q81.
The Balmer series of the hydrogen spectrum lies mainly in the:
Q82.
The ionization energy of a hydrogen atom in its ground state is:
Q83.
The shortest wavelength (series limit) of the Lyman series of hydrogen (1/R ≈ 91.2 nm) is:
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