**Core Concept**
The question pertains to the radiopacity of renal stones, which is a crucial aspect in their diagnosis and management. Radiopacity refers to the ability of a substance to be visible on radiographic images, such as X-rays or CT scans.

**Why the Correct Answer is Right**
Approximately 90% of renal stones are radiopaque, meaning they can be seen on plain radiographs or CT scans. This is because most renal stones are composed of calcium salts, such as calcium oxalate, calcium phosphate, or uric acid, which are denser and more opaque than soft tissues. The high radiopacity of these stones facilitates their detection and localization, allowing for targeted treatment and minimization of complications.

**Why Each Wrong Option is Incorrect**
**Option A:** 10% is incorrect as it significantly underestimates the radiopacity of renal stones. The actual percentage is much higher, reflecting the high density of calcium salts in most stones.
**Option B:** 25% is incorrect as it still falls short of the actual percentage. While some renal stones may be radiolucent, the majority are indeed radiopaque.

**Clinical Pearl / High-Yield Fact**
It's essential to note that radiolucent stones, which are less than 10% of the total, may be composed of struvite, cystine, or uric acid. These stones often require specialized imaging techniques, such as ultrasound or CT scans with non-contrast settings, for accurate detection.

**✓ Correct Answer: D. 90%**