Which condition must be met for an electron in an atom to undergo an energy level transition?

• A. The electron must collide with another electron.
• B. The atom must be at absolute zero temperature.
• C. The atom must be in a vacuum.
• D. The atom must absorb or emit a photon with energy equal to the difference between the two energy levels.

Answer: (D)

Verified step by step guidance

1. Understand that electrons in an atom occupy specific energy levels or orbitals, each with a defined energy value.
2. Recognize that for an electron to move from one energy level to another, it must gain or lose energy exactly equal to the difference between those two levels.
3. Recall that energy transfer in atoms typically occurs through the absorption or emission of photons, where a photon carries a discrete amount of energy given by \(E = h \nu\), with \(h\) being Planck's constant and \(\nu\) the frequency of the photon.
4. Therefore, the condition for an electron to undergo an energy level transition is that the atom must absorb or emit a photon whose energy matches the energy gap between the initial and final energy levels.
5. Note that other options like collisions with electrons, absolute zero temperature, or vacuum conditions are not necessary conditions for such transitions to occur.