**Core Concept**
The question tests the student's knowledge of penicillin pharmacology, specifically their ability to identify penicillins that can be administered intravenously (i.v.). Penicillins are a group of beta-lactam antibiotics that work by inhibiting bacterial cell wall synthesis.

**Why the Correct Answer is Right**
Among the penicillins, some are more stable in aqueous solution and can be given by i.v. route. This is because they are less susceptible to hydrolysis by beta-lactamases and are more resistant to chemical degradation. **Benztropine** is not a penicillin; it's an anticholinergic used in the treatment of Parkinson's disease. **Ampicillin** and **Amoxicillin** are penicillins that are generally not suitable for i.v. administration due to their instability in aqueous solution. In contrast, **Penicillin G** (also known as benzylpenicillin) is a narrow-spectrum penicillin that can be administered i.v. due to its stability in aqueous solution.

**Why Each Wrong Option is Incorrect**
* **Option A:** Benztropine is not a penicillin and is not used for antibacterial purposes; it's used to treat Parkinson's disease.
* **Option B:** Ampicillin is a broad-spectrum penicillin that is generally not suitable for i.v. administration due to its instability in aqueous solution.
* **Option C:** Amoxicillin is a broad-spectrum penicillin that is generally not suitable for i.v. administration due to its instability in aqueous solution.

**Clinical Pearl / High-Yield Fact**
When administering penicillins by i.v. route, it's essential to use a solution that is isotonic with blood to prevent hemolysis. Penicillin G is typically administered in a solution that is isotonic with blood, making it a safe choice for i.v. administration.

**Correct Answer:** C. Penicillin G (Benzylpenicillin)