Final answer:
Mass spectrometry is the technique used to determine the amino acid sequence of a protein or peptide and is critical in the field of proteomics for protein analysis.
Step-by-step explanation:
The technique used to determine the amino acid sequence of a protein or peptide is C) Mass spectrometry. This protein analysis method allows scientists to identify and characterize molecules by analyzing very small samples. While X-ray crystallography and Nuclear magnetic resonance (NMR) are used to determine the three-dimensional structure of proteins, mass spectrometry is analogous to DNA sequencing for determining the sequencing of proteins. Both protein microarrays and various sequencing techniques contribute to the broader field of proteomics, with large-scale applications and computer software playing roles in data analysis.