Step 1: Concept
Acidic amino acids have an extra carboxyl (-COOH) group in their side chain.
Step 2: Analysis
- Arg (Arginine) and Lys (Lysine) are basic.
- Met (Methionine) is neutral/sulfur-containing.
- Asp (Aspartic acid) and Glu (Glutamic acid) are acidic.
Step 3: Conclusion
Hence, Asp is the acidic amino acid.
Final Answer: (D)