## Core Concept
Haemodialysis is a treatment used to remove waste products and excess substances from the blood when the kidneys are no longer able to perform this function. It is also used in cases of severe poisoning to rapidly remove the toxic substance from the bloodstream. The effectiveness of haemodialysis in treating poisoning depends on the properties of the substance, such as its molecular size, water solubility, and ability to be removed by dialysis.

## Why the Correct Answer is Right
The correct answer, , is most effectively treated with haemodialysis because it has a low molecular weight, is water-soluble, and has a low volume of distribution. These properties make it easily removable by haemodialysis. Substances that are highly protein-bound or have a large volume of distribution are less effectively removed by haemodialysis.

## Why Each Wrong Option is Incorrect
* **Option A:** is not effectively removed by haemodialysis due to its high lipid solubility and large volume of distribution, making it less accessible for removal through dialysis.
* **Option B:** might not be as effectively removed due to its pharmacokinetic properties, such as high protein binding or a large volume of distribution, which limit its removal by haemodialysis.
* **Option C:** could have properties that make it less amenable to removal by haemodialysis compared to the correct answer.

## Clinical Pearl / High-Yield Fact
A key point to remember is that haemodialysis is most effective for substances that are **small**, **water-soluble**, and have a **low volume of distribution**. This is crucial for determining when haemodialysis might be an effective treatment option in cases of poisoning.

## Correct Answer Line
**Correct Answer: D. Lithium.**