**Core Concept**
The question is testing the student's knowledge of amino acid classification. Amino acids can be broadly categorized into non-polar (neutral), polar (uncharged), and acidic or basic. Acidic amino acids are those with a side chain that carries a negative charge at physiological pH, often due to the presence of a carboxyl (-COOH) group.

**Why the Correct Answer is Right**
The correct answer is an acidic amino acid because it has a side chain with a carboxyl group (-COOH). This group is deprotonated at physiological pH, resulting in a negatively charged side chain. This characteristic is crucial for the molecule's function in biological systems, including its role in protein structure and function.

**Why Each Wrong Option is Incorrect**
* **Option A:** This amino acid is a non-polar (neutral) amino acid, lacking a charged side chain at physiological pH.
* **Option B:** This amino acid is a basic amino acid, with a side chain that carries a positive charge at physiological pH due to the presence of an amino group (-NH2).
* **Option D:** This amino acid is a polar (uncharged) amino acid, with a side chain that may participate in hydrogen bonding but does not carry a charge at physiological pH.

**Clinical Pearl / High-Yield Fact**
To remember the difference between acidic, basic, and neutral amino acids, recall that acidic amino acids have a side chain with a carboxyl (-COOH) group, basic amino acids have a side chain with an amino group (-NH2), and neutral amino acids lack a charged side chain.

**Correct Answer:** C. Aspartic acid