## **Core Concept**
Carbon monoxide (CO) poisoning is a significant cause of morbidity and mortality worldwide. It occurs through inhalation of CO, which binds to hemoglobin with high affinity, forming carboxyhemoglobin (COHb) and reducing oxygen delivery to tissues. Post-mortem diagnosis of CO poisoning involves identifying specific signs and changes in the body.

## **Why the Correct Answer is Right**
The correct answer involves understanding the pathophysiological changes and manifestations of CO poisoning.
- **a) Blood thin and red coloured**: This is correct because CO poisoning results in the formation of carboxyhemoglobin, which gives the blood a bright red color.
- **b) Congestion of all organs**: This is also a feature of CO poisoning due to the tissue hypoxia caused by reduced oxygen delivery.
- **d) Blister on skin**: Skin blisters can occur in CO poisoning due to tissue damage and hypoxia.

## **Why Each Wrong Option is Incorrect**
- **Option C: Cyanosis**: This is incorrect because cyanosis, a bluish discoloration of the skin and mucous membranes, typically indicates a problem with oxygenation or circulation. However, in CO poisoning, the blood appears bright red due to carboxyhemoglobin, and cyanosis is not a characteristic finding.
- **Option E: Parkinsonism**: While CO poisoning can cause neurological damage, including Parkinson-like symptoms due to damage to the basal ganglia, it is not a direct post-mortem diagnostic criterion.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that CO poisoning can mimic other conditions, making diagnosis challenging. Post-mortem findings, along with scene investigation and laboratory confirmation of COHb levels, are crucial for diagnosis. A classic finding is the "cherry-red" discoloration of the skin, but this is not listed among the options.

## **Correct Answer: B.**