**Core Concept**
A second-generation cephalosporin is a type of β-lactam antibiotic that exhibits a broader spectrum of activity compared to first-generation cephalosporins, with enhanced stability against β-lactamase enzymes produced by Gram-negative bacteria. Oral administration of these antibiotics requires chemical modifications to enhance their stability and absorption in the gastrointestinal tract.

**Why the Correct Answer is Right**
Cefaclor is a second-generation cephalosporin that has been modified to be more resistant to hydrolysis by β-lactamases, allowing it to be effective against a wider range of Gram-negative bacteria. Its oral bioavailability is also improved due to the presence of a methyl group at the 7α-position, which enhances its absorption in the gastrointestinal tract. Cefaclor is commonly used to treat respiratory tract infections, skin infections, and urinary tract infections.

**Why Each Wrong Option is Incorrect**
**Option A:** Cefipime is a fourth-generation cephalosporin, which has a broader spectrum of activity and enhanced stability against β-lactamases compared to second-generation cephalosporins. It is typically administered intravenously due to its poor oral bioavailability.
**Option B:** Cephalothin is a first-generation cephalosporin, which has limited activity against Gram-negative bacteria and is not suitable for oral administration due to its poor stability in the gastrointestinal tract.
**Option D:** Cefadroxil is a first-generation cephalosporin, which has limited activity against Gram-negative bacteria and is not as stable as second-generation cephalosporins like cefaclor.

**Clinical Pearl / High-Yield Fact**
When selecting an oral cephalosporin, it's essential to consider the patient's specific infection and the antibiotic's spectrum of activity. Second-generation cephalosporins like cefaclor are often preferred for respiratory tract infections, while fourth-generation cephalosporins like cefipime may be used for more severe or resistant infections.

✓ Correct Answer: C. Cefaclor