## Core Concept
The question tests the knowledge of nephrotoxicity associated with aminoglycosides, a class of antibiotics used to treat severe bacterial infections. Aminoglycosides can cause nephrotoxicity, which is a significant concern in clinical practice. The degree of nephrotoxicity varies among different aminoglycosides.

## Why the Correct Answer is Right
Among the aminoglycosides, **Gentamicin** is known for having a higher nephrotoxic potential compared to others like Tobramycin, Amikacin, and Streptomycin. This is because gentamicin accumulates in the renal cortex to a greater extent and can cause damage to the proximal convoluted tubules. The mechanism involves the uptake of gentamicin by renal tubular cells, leading to cellular injury and death.

## Why Each Wrong Option is Incorrect
* **Option A (Tobramycin):** While tobramycin is also nephrotoxic, its nephrotoxic potential is generally considered lower than that of gentamicin. Tobramycin is often chosen for its lower nephrotoxicity profile when treating patients at risk for renal impairment.
* **Option C (Amikacin):** Amikacin has a lower nephrotoxicity profile compared to gentamicin. It is sometimes preferred in patients with pre-existing renal issues or when trying to minimize nephrotoxicity.
* **Option D (Streptomycin):** Streptomycin is the least nephrotoxic among the aminoglycosides listed. It was the first aminoglycoside discovered and has been used for decades, particularly for treating tuberculosis.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **gentamicin** has a notably high risk of nephrotoxicity among aminoglycosides. Clinicians often monitor renal function closely in patients receiving gentamicin and consider alternatives when prolonged therapy is anticipated or in patients with pre-existing renal disease.

## Correct Answer: B. Gentamicin.