The flame color observed for Na+ in a flame test is which color?

• A. Red
• B. Yellow
• C. Lilac
• D. Orange

Answer: (B)

Flame colors come from photons emitted when excited electrons drop to lower energy levels in the atoms present. Sodium has a very strong and distinct emission at about 589 nanometers, the Na D-line, which falls in the yellow part of the spectrum. That bright yellow emission dominates what you see in the flame, so the observed color is yellow. Other elements give different hues (for example, lithium looks red, potassium lilac, calcium orange-red), but the sodium line is so intense that yellow is the characteristic flame color you detect.