**Core Concept**
Third-generation cephalosporins are a class of β-lactam antibiotics characterized by their broad-spectrum activity against Gram-negative bacteria. They are further divided into different generations based on their spectrum of activity and stability to β-lactamases. Oral administration of third-generation cephalosporins is limited due to their poor absorption in the gastrointestinal tract.

**Why the Correct Answer is Right**
Cefixime, a third-generation cephalosporin, is unique in that it can be administered orally due to its high bioavailability and stability in the acidic environment of the stomach. This allows it to be absorbed effectively in the small intestine, making it a suitable option for oral administration. Cefixime's mechanism of action involves inhibiting cell wall synthesis in bacteria by binding to penicillin-binding proteins (PBPs), leading to bacterial cell lysis.

**Why Each Wrong Option is Incorrect**
**Option A:** Ceftriaxone is a third-generation cephalosporin, but it is typically administered parenterally (intravenously or intramuscularly) due to its poor oral bioavailability.
**Option B:** Cefotaxime is another third-generation cephalosporin, but it is not suitable for oral administration due to its instability in the acidic environment of the stomach.
**Option C:** Cefdinir is a fourth-generation cephalosporin, not a third-generation cephalosporin, and is also suitable for oral administration.

**Clinical Pearl / High-Yield Fact**
Remember that oral bioavailability is crucial for oral antibiotics, and not all third-generation cephalosporins are created equal in this regard.

**Correct Answer: C. Cefixime**