**Core Concept**
The triangular cord sign on ultrasound is a characteristic finding in biliary atresia, a congenital condition where the bile ducts are absent or severely malformed, leading to obstructive jaundice in neonates.

**Why the Correct Answer is Right**
In biliary atresia, the ultrasound shows a "triangular cord" or "crescentic" structure in the liver parenchyma, representing the dilated extrahepatic bile ducts. This sign is due to the absence of normal bile flow, causing bile to accumulate and form a thin, triangular echogenic band. It is highly specific for biliary atresia and appears early in the disease course, often before clinical symptoms manifest.

**Why Each Wrong Option is Incorrect**
Option A: Galactosemia presents with metabolic derangements and hepatomegaly, but not the triangular cord sign. It is a metabolic disorder, not a biliary obstruction.
Option C: Hepatitis (e.g., viral) causes hepatocellular injury and elevated transaminases, but does not produce the triangular cord sign on ultrasound.
Option D: The triangular cord sign is not seen in any of the listed conditions except biliary atresia, so "none" is incorrect.

**Clinical Pearl / High-Yield Fact**
The triangular cord sign on ultrasound is a key diagnostic clue for biliary atresia and should prompt immediate referral for surgical evaluation. Early detection improves surgical outcomes, as the condition is treatable with Kasai portoenterostomy if diagnosed early.

✓ Correct Answer: B. Biliary atresia