Which wavelengths appear in the emission spectrum of an atom?

• A. Only the wavelengths corresponding to allowed electronic transitions between energy levels
• B. Only ultraviolet wavelengths
• C. Only infrared wavelengths
• D. All possible wavelengths across the electromagnetic spectrum

Answer: (A)

Verified step by step guidance

1. Understand that an emission spectrum of an atom is produced when electrons transition from higher energy levels to lower energy levels, releasing energy in the form of photons.
2. Recall that the energy of the emitted photon corresponds exactly to the difference between the two energy levels involved in the transition, given by the formula \(\Delta E = h \nu = \frac{hc}{\lambda}\), where \(h\) is Planck's constant, \(\nu\) is frequency, \(c\) is the speed of light, and \(\lambda\) is the wavelength.
3. Recognize that only certain discrete energy levels are allowed in an atom, so only specific energy differences (and thus specific wavelengths) can be emitted.
4. Conclude that the emission spectrum consists only of wavelengths corresponding to these allowed electronic transitions, not all possible wavelengths or limited to a single region like ultraviolet or infrared.
5. Therefore, the emission spectrum shows discrete lines at wavelengths corresponding to allowed electronic transitions between energy levels.