Final answer:
The source of radiant energy in atomic absorption spectrophotometry is the absorption of light by ground-state atoms to produce an excited state.
Step-by-step explanation:
The source of radiant energy in atomic absorption spectrophotometry is the absorption of light by ground-state atoms to produce an excited state, which is then detected and analyzed. Atomic absorption spectrophotometry is a technique used to determine the concentrations of elements in a sample by measuring the absorption of light at specific wavelengths.