Free Spectrum of Hydrogen MCQs with Answers

1. The lines of the Balmer series in the hydrogen spectrum are produced when an electron falls to which energy level?

• A. n = 1
• B. n = 2
• C. n = 3
• D. n = 4

Explanation: The Balmer series arises from transitions ending at n equal to 2 and it is the only hydrogen series that falls in the visible region, which is why it was discovered first. Transitions ending at n equal to 1 give the Lyman series in the ultraviolet, and those ending at n equal to 3 give the Paschen series in the infrared.

2. The line spectrum of hydrogen provides direct evidence that

• A. electrons can have any energy value
• B. electron energies inside an atom are quantised
• C. the nucleus contains neutrons
• D. hydrogen atoms contain more than one electron

Explanation: A hot gas emits light only at particular wavelengths, producing separate bright lines instead of a continuous band, and each line corresponds to one fixed energy difference between two levels. If electrons could take any energy the spectrum would be continuous. Nothing in the spectrum speaks to the neutron, and hydrogen has exactly one electron.

3. Bohr's model explained the hydrogen spectrum by proposing that

• A. electrons can occupy any orbit
• B. electrons occupy fixed energy levels and emit a photon when moving to a lower one
• C. the nucleus emits light directly
• D. electrons spiral into the nucleus

Explanation: Restricting electrons to discrete levels means only certain energy differences are available, so only certain frequencies appear, which is exactly what a line spectrum shows. Classical physics predicted a continuous spectrum and an electron spiralling into the nucleus within a fraction of a second. The photon energy equals the difference between the two levels.

4. The lines of the Balmer series in the hydrogen spectrum arise from transitions ending at

• A. n equals 1
• B. n equals 2
• C. n equals 3
• D. n equals 4

Explanation: Transitions to the second level release energies corresponding to visible light, which is why the Balmer lines are the ones seen through a spectroscope. Transitions to the ground state form the ultraviolet Lyman series and those to the third level the infrared Paschen series. The series is identified by the level the electron lands on, not the one it starts from.