**Core Concept**
Biliary atresia is a congenital condition where there is a blockage or absence of the bile ducts, leading to liver damage and cirrhosis if left untreated. In infants undergoing surgery for biliary atresia, it is crucial to choose an anaesthetic agent that does not exacerbate liver function or increase the risk of hepatotoxicity.

**Why the Correct Answer is Right**
Halothane is a potent inhalational anaesthetic agent that can cause hepatitis and hepatotoxicity, particularly in infants and children. This is due to its metabolism by the cytochrome P450 enzyme system in the liver, which can lead to the formation of toxic metabolites. In infants with biliary atresia, the liver is already compromised, and the use of halothane could further exacerbate liver damage.

**Why Each Wrong Option is Incorrect**
* **Option A:** Thiopentone is a barbiturate-based intravenous anaesthetic agent that is commonly used in pediatric anesthesia. It does not have any known hepatotoxic effects and is not contraindicated in biliary atresia.
* **Option C:** Propofol is a popular intravenous anaesthetic agent known for its anti-emetic properties and rapid onset of action. It is not associated with liver toxicity and can be safely used in infants undergoing surgery for biliary atresia.
* **Option D:** Sevoflurane is another inhalational anaesthetic agent that is widely used in pediatric anesthesia. It is less hepatotoxic than halothane and is often preferred in children due to its pleasant odor and rapid recovery profile.

**Clinical Pearl / High-Yield Fact**
When choosing an anaesthetic agent for infants with biliary atresia, it is essential to consider the potential for hepatotoxicity and choose an agent that minimizes this risk. Halothane should be avoided in these patients due to its association with hepatitis and hepatotoxicity.

✓ Correct Answer: B. Halothane