**Core Concept**
An alpha helix is a fundamental secondary structure of proteins, characterized by a spiral conformation with hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another, four residues away. This structure is stabilized by the hydrogen bonding between the amino acids, allowing for a compact and stable arrangement of the polypeptide chain.

**Why the Correct Answer is Right**
In an alpha helix, the first turn accommodates approximately 3.6 amino acid residues. The amino acid that is suitably accommodated within the first turn is the third amino acid residue, as it allows for the formation of a stable hydrogen bond between the carbonyl oxygen of the second residue and the amide hydrogen of the third residue. This arrangement enables the alpha helix to maintain its structural integrity and stability.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as the first amino acid residue is not suitably accommodated within the first turn of an alpha helix, as it does not participate in hydrogen bonding.
* **Option B:** This option is incorrect as the second amino acid residue is not the most stable position within the first turn, as it is involved in hydrogen bonding with the first residue, creating a less stable arrangement.
* **Option D:** This option is incorrect as the amino acid located at the N-terminus of the protein chain is not accommodated within the first turn of an alpha helix, as it does not participate in hydrogen bonding.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the stability of an alpha helix depends on the formation of hydrogen bonds between amino acid residues, which are crucial for maintaining the structure and function of proteins.

**Correct Answer:** C.