## **Core Concept**
Cadaveric lividity, also known as livor mortis, refers to the discoloration of the skin due to the pooling of blood in the dependent parts of the body after death. The color of lividity can sometimes indicate the cause of death, particularly in cases of poisoning.

## **Why the Correct Answer is Right**
The bluish-green color of cadaveric lividity is characteristic of **hydrogen sulfide** or **cyanide** poisoning, but more specifically, a bluish-green discoloration is highly suggestive of hydrogen sulfide poisoning. Hydrogen sulfide disrupts cellular respiration, similar to cyanide, but the greenish tint comes from the formation of sulfmethemoglobin and biliverdin due to the breakdown of hemoglobin.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While certain substances can cause discoloration, there's no common poison that directly results in a characteristic bluish-green lividity as described.
- **Option B:** This option is not specified, but generally, most poisonings do not result in such a distinct bluish-green coloration of lividity.
- **Option C:** Similarly, without specification, it's hard to directly refute, but typical poisons do not cause this specific color change.
- **Option D:** Assuming this is not the correct answer based on the provided information.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **hydrogen sulfide poisoning** can cause a distinctive **bluish-green** discoloration of the skin due to the formation of specific pigments. This is a rare but classic sign that can help in the post-mortem diagnosis of poisoning.

## **Correct Answer:** C. Hydrogen sulphide.