## **Core Concept**
The question pertains to the composition of gallstones found in the gallbladder, specifically the pale yellow type. Gallstones can be classified based on their composition into cholesterol stones, pigment stones (bilirubin stones), and mixed stones. The predominant constituent of pale yellow gallstones is typically cholesterol.

## **Why the Correct Answer is Right**
The correct answer, **B. Cholesterol**, is right because pale yellow gallstones are primarily composed of cholesterol. These cholesterol stones are the most common type of gallstone in many parts of the world, especially in Western countries. They are usually pale yellow in color and are composed mainly of cholesterol (> 90% cholesterol by weight). The formation of cholesterol stones is associated with an imbalance in the composition of bile, including supersaturation of cholesterol, which leads to the precipitation of cholesterol crystals.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while bilirubin and its derivatives can form gallstones (pigment stones), they are typically darker in color and not the predominant constituent of pale yellow stones.
- **Option C:** This option is incorrect because mixed stones, which contain a combination of cholesterol and bilirubin, may have various colors but are not specified as predominantly pale yellow due to their mixed composition.
- **Option D:** This option is incorrect because while other substances can be present in gallstones, cholesterol is specifically known to form pale yellow stones.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that cholesterol gallstones are often associated with obesity, female gender, and a diet high in cholesterol and low in fiber. They are also more likely to occur in individuals with a condition known as "lithogenic bile," which promotes the formation of cholesterol stones.

## **Correct Answer:** . Cholesterol