## **Core Concept**
Pigment stones, also known as pigment gallstones, are a type of gallstone primarily composed of bilirubin and calcium salts. They are one of the two main types of gallstones, the other being cholesterol stones. Pigment stones are often associated with hemolytic disorders.

## **Why the Correct Answer is Right**
The correct answer, **bilirubin and calcium salts**, is right because pigment stones are indeed formed from these components. Bilirubin, a yellow pigment produced during the breakdown of hemoglobin in the liver, can combine with calcium salts to form calcium bilirubinate, which is the main constituent of pigment stones. This process is often seen in conditions associated with increased bilirubin production, such as hemolytic diseases (e.g., sickle cell anemia).

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify the correct composition of pigment stones.
- **Option B:** This option is incorrect as it does not accurately represent the composition of pigment stones.
- **Option C:** This option is incorrect because, although cholesterol is a component of another type of gallstone (cholesterol stones), it is not a primary component of pigment stones.

## **Clinical Pearl / High-Yield Fact**
A key clinical correlation to remember is that pigment stones are often associated with **hemolytic disorders**, such as sickle cell disease, and **infected bile** due to the presence of bacteria that deconjugate bilirubin glucuronides, leading to the formation of unconjugated bilirubin which can precipitate out as pigment stones.

## **Correct Answer:** D. bilirubin and calcium salts.