Which of the following instruments is used to find out absorption...

Fourier transform Infrared (FTIR) spectrophotometer is used to identify functional groups in organic molecules. Different functional groups absorb characteristic frequencies of infrared radiation, which causes vibrational transitions in the bonds.

X-ray diffractometer is used to determine the crystal structure of a solid.

UV-visible spectrophotometer is used to study electronic transitions, typically in conjugated systems or transition metal complexes.

Scanning electron microscope is used to study the surface morphology and topography of a sample.

Therefore, FTIR is the correct instrument for finding the absorption of functional groups.

Answer: Fourier transform Infrared spectrophotometer