**Core Concept**
Penicillin G, also known as benzylpenicillin, is a narrow-spectrum beta-lactam antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs) on the bacterial cell wall. This action disrupts the bacterial cell wall's integrity, ultimately leading to cell lysis and death.

**Why the Correct Answer is Right**
The correct answer is **D**. Penicillin G is not metabolized by the liver, but rather is excreted unchanged in the urine. This is due to its low lipid solubility and its ability to be reabsorbed from the renal tubules. As a result, patients with renal impairment may experience prolonged half-lives and increased toxicity of penicillin G.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect as penicillin G is indeed a narrow-spectrum antibiotic, effective against Gram-positive cocci, such as Staphylococcus aureus and Streptococcus pneumoniae.
**Option B:** This statement is incorrect as penicillin G is indeed a beta-lactam antibiotic, which inhibits bacterial cell wall synthesis.
**Option C:** This statement is incorrect as penicillin G is indeed a bactericidal agent, which kills bacteria by disrupting their cell walls.

**Clinical Pearl / High-Yield Fact**
When administering penicillin G, it's essential to maintain adequate renal function to prevent accumulation and toxicity. Monitoring renal function and adjusting the dose accordingly is crucial in patients with renal impairment.

**Correct Answer:** D.