**Core Concept**
Third-generation cephalosporins are characterized by enhanced penetration into the central nervous system (CNS), broader spectrum against gram-negative bacteria, and reduced activity against gram-positive organisms compared to first- and second-generation agents. They are often used for serious infections like sepsis, meningitis, and urinary tract infections.

**Why the Correct Answer is Right**
Ceftriaxone, cefotaxime, and ceftizoxime are all third-generation cephalosporins with strong activity against gram-negative pathogens, including *Enterobacter*, *Klebsiella*, and *Pseudomonas* (especially ceftriaxone and cefotaxime). Cefuroxime, however, is classified as a **second-generation cephalosporin** due to its intermediate gram-negative coverage and limited CNS penetration. It has less activity against *Pseudomonas* and is primarily used for respiratory tract infections.

**Why Each Wrong Option is Incorrect**
Option A: Ceftriaxone is a third-generation cephalosporin with excellent CNS penetration and broad gram-negative coverage.
Option B: Cefotaxime is a third-generation agent with strong activity against *Enterobacteriaceae* and *Pseudomonas*.
Option C: Ceftizoxime is a third-generation cephalosporin with activity against *Pseudomonas* and good CNS penetration.
Option D: Cefuroxime is **not** a third-generation cephalosporin — it belongs to the second generation and has limited gram-negative coverage compared to third-gen agents.

**Clinical Pearl / High-Yield Fact**
Remember the mnemonic: **"Third-gen: Ceftriaxone, Cefotaxime, Ceftizoxime"** — all have good gram-negative coverage and CNS penetration. **Cefuroxime** is a second-gen cephalosporin and should not be confused with third-gen agents.

✓ Correct Answer: D. Cefuroxime