## Core Concept
Penicillin G, also known as benzylpenicillin, is a narrow-spectrum β-lactam antibiotic of the penicillin class. It is effective against Gram-positive bacteria, some Gram-negative bacteria, and certain anaerobic bacteria. Its mechanism of action involves inhibiting bacterial cell wall synthesis.

## Why the Correct Answer is Right
The correct statement about Penicillin G is that it is **primarily effective against Gram-positive bacteria and certain Gram-negative cocci**. This effectiveness is due to its mechanism of action, which involves binding to penicillin-binding proteins (PBPs) located inside the bacterial cell wall, resulting in the disruption of the cell wall synthesis process, ultimately leading to cell lysis and death. Penicillin G is particularly effective against *Streptococcus pneumoniae*, *Streptococcus pyogenes*, and *Neisseria gonorrhoeae*.

## Why Each Wrong Option is Incorrect
- **Option A:** This option might claim that Penicillin G has a broad spectrum of activity, which is incorrect. Penicillin G is considered a narrow-spectrum antibiotic because it targets a limited range of bacteria, primarily Gram-positive and some Gram-negative cocci.
- **Option B:** If this option suggests that Penicillin G is stable in acidic pH, it would be incorrect. Penicillin G is unstable in acidic environments, which affects its absorption and necessitates its administration parenterally or orally with buffering agents.
- **Option C:** This option might state that Penicillin G is effective against a wide range of Gram-negative bacteria, which is not accurate. While it does have some activity against certain Gram-negative cocci, its effectiveness against Gram-negative bacilli is generally limited due to the presence of β-lactamase enzymes in many Gram-negative bacteria.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Penicillin G is **short-acting** and requires frequent dosing to maintain therapeutic levels. It is also important to note that resistance to Penicillin G can occur through various mechanisms, including the production of β-lactamases, alterations in PBPs, and decreased uptake or increased efflux of the antibiotic.

## Correct Answer Line
**Correct Answer: D.** (Assuming D is the statement that accurately describes Penicillin G's effectiveness against Gram-positive bacteria and certain Gram-negative cocci.)