Spectroscopy is categorized into two main groups. Which list correctly pairs examples for emission and absorption methods?

• A. Emission (fluorometer, AES, flame photometer) and Absorption (UV/Vis/IR spectroscopy, NMRS, AAS)
• B. Emission (UV/Vis/IR spectroscopy) and Absorption (fluorometer)
• C. Scattering and Emission
• D. Reflectance and Absorption

Answer: (A)

Spectroscopy techniques are grouped by whether the signal comes from light energy emitted by the sample or light energy absorbed by the sample. Emission methods detect light that is produced when excited species release energy. Fluorometers measure the fluorescence emitted by excited molecules, atomic emission spectroscopy (AES) detects light emitted by excited atoms or ions in a flame or plasma, and flame photometry relies on light emitted by excited species in the flame. Absorption methods quantify how much light is taken up by the sample at specific wavelengths. UV/Vis/IR spectroscopy measures absorption of light in those regions, atomic absorption spectroscopy (AAS) gauges absorption by vaporized atoms, and nuclear magnetic resonance spectroscopy (NMRS) involves the absorption of radiofrequency energy by nuclei in a magnetic field to produce resonances. The other options mix categories (for example, assigning UV/Vis/IR to emission or grouping NMRS with non-absorption methods), which doesn’t fit the standard emission versus absorption distinction.