**Core Concept**
The question pertains to the classification of amino acids based on their chemical properties, specifically their basic nature. Amino acids can be categorized into three main groups: acidic, basic, and neutral, depending on the presence and type of functional groups attached to the alpha carbon.

**Why the Correct Answer is Right**
Among the given options, the correct answer is the amino acid with the highest pKa value for its side-chain, indicating a higher degree of basicity. This is due to the presence of a guanidinium group (-G-) in the side-chain, which is a strong electron-withdrawing group, thereby increasing the pKa value of the alpha-amino group. This makes the amino acid more basic in nature.

**Why Each Wrong Option is Incorrect**
**Option A:** This amino acid is actually an acidic amino acid due to the presence of a carboxyl group (-COOH) in its side-chain, making it a candidate for the opposite category.
**Option B:** This amino acid is a neutral amino acid, lacking any strong electron-withdrawing or electron-donating groups in its side-chain.
**Option C:** This amino acid is also a neutral amino acid, similar to Option B, with no strong basic or acidic properties in its side-chain.

**Clinical Pearl / High-Yield Fact**
Remember the mnemonic "GABA" to associate with the basic amino acid: Guanidinium (Arginine), Alanine (neutral), and Beta-Alanine (neutral). This can help you distinguish between basic and neutral amino acids on the exam.

**Correct Answer:** C. Arginine.