**Core Concept**
The question is testing the concept of acid-base chemistry and the dissociation constant (pKa) of amino acids. Physiological pH is around 7.4, and an amino acid with a pKa close to this value will be more ionized and thus more likely to be in its charged form in the body.

**Why the Correct Answer is Right**
Histidine is an amino acid with a pKa of approximately 6.0-7.0, making it one of the most ionizable amino acids at physiological pH. This is due to the presence of an imidazole side chain, which is a weak base and can accept a proton, thereby increasing the pH of the surrounding environment. As a result, histidine is more likely to be in its positively charged form at physiological pH, which is essential for its role in various biological processes, including enzyme function and protein-protein interactions.

**Why Each Wrong Option is Incorrect**
**Option A:** **Glutamic acid** has a pKa of around 4.25, which is too low to be relevant at physiological pH. Its side chain is a carboxylic acid group, making it a strong acid that is mostly in its charged form at physiological pH.
**Option B:** **Aspartic acid** has a pKa of around 3.9, which is also too low to be relevant at physiological pH. Like glutamic acid, its side chain is a carboxylic acid group, making it a strong acid that is mostly in its charged form at physiological pH.
**Option C:** **Lysine** has a pKa of around 10.5, which is too high to be relevant at physiological pH. Its side chain is a basic group, making it a weak base that is mostly in its uncharged form at physiological pH.

**Clinical Pearl / High-Yield Fact**
Histidine is an essential amino acid, which means that it cannot be synthesized by the human body and must be obtained through the diet. A deficiency in histidine can lead to impaired growth and development, particularly in children.

**Correct Answer:** C. Lysine