Photoelectric Effect and Line Spectra (4E) Practice Test

A researcher studies a one-electron atom that emits a line spectrum similar to hydrogen. When the nucleus is replaced with a different isotope (same atomic number, different mass), the bright emission lines are observed at essentially the same wavelengths within the instrument’s resolution. Which statement best accounts for this result using the principle of quantized energy levels?

A researcher observes that a hydrogen discharge tube emits a line at 656 nm. When the tube is cooled, the line remains at 656 nm but becomes dimmer. Which explanation is most consistent with the core principle of line spectra?