**Core Concept**
Radiopaque gallstones are a type of gallstone that contains sufficient amounts of calcium or other minerals to be visible on plain X-rays. These stones are typically composed of calcium carbonate, calcium phosphate, or other calcium salts.

**Why the Correct Answer is Right**
Only a small percentage of gallstones are radiopaque, as most gallstones are composed of cholesterol, which is not visible on X-rays. The calcium content in radiopaque gallstones allows them to be visualized on plain radiographs, making them detectable via this imaging modality. This characteristic is particularly useful in clinical settings where X-rays are readily available and can aid in the diagnosis of gallstone disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is likely incorrect as the percentage of radiopaque gallstones is relatively low, and it's not a commonly cited value in medical literature.
* **Option B:** This option might be too high, as radiopaque gallstones are a minority among all gallstones.
* **Option C:** This option is incorrect as it is a lower percentage compared to the actual value, which is a significant portion but not the majority.

**Clinical Pearl / High-Yield Fact**
It's essential to note that while radiopaque gallstones can be visualized on X-rays, many gallstones are not visible on plain films and may require additional imaging modalities like ultrasound or CT scans for detection.

**Correct Answer:** C. 10%