**Core Concept**
Iso-osmolar contrast media are non-ionic, monomeric agents used in radiographic imaging to reduce the risk of nephrotoxicity. They have an osmolarity similar to that of blood, making them suitable for patients with renal impairment.

**Why the Correct Answer is Right**
The correct answer is a type of contrast agent that maintains an osmotic balance with blood, thereby minimizing the risk of renal damage. Iso-osmolar agents like iopamidol and iohexol are metabolized in the liver and excreted in the bile, reducing their nephrotoxic potential. This property makes them particularly useful in patients with pre-existing renal disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect as it is a high-osmolar agent, which can cause renal vasoconstriction and increase the risk of nephrotoxicity.
* **Option B:** This is incorrect as it is a low-osmolar agent, but not iso-osmolar, and may still cause some degree of renal impairment.
* **Option D:** This is incorrect as it is a type of contrast agent that is not commonly used in clinical practice.

**Clinical Pearl / High-Yield Fact**
When choosing a contrast agent, it is essential to consider the patient's renal function and the risk of nephrotoxicity. Iso-osmolar agents like iopamidol and iohexol are generally safer options for patients with renal impairment.

**Correct Answer:** C. Iohexol