**Core Concept**
In post-hepatic jaundice, also known as obstructive jaundice, the liver is structurally intact but the flow of bile is obstructed, typically due to a blockage in the bile ducts. This obstruction prevents conjugated bilirubin from entering the intestines, but does not affect the liver's ability to conjugate bilirubin.

**Why the Correct Answer is Right**
The conjugation process of bilirubin in the liver involves the enzyme UDP-glucuronyltransferase, which converts unconjugated bilirubin into conjugated bilirubin. In post-hepatic jaundice, the liver's cellular machinery remains functional, and the conjugation process continues unabated. Consequently, the concentration of conjugated bilirubin in the blood increases, whereas the concentration of unconjugated bilirubin remains relatively low. This is because the liver is able to conjugate bilirubin normally, but the obstructed bile ducts prevent the conjugated bilirubin from being excreted into the intestines.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased destruction of red blood cells would lead to an increase in both unconjugated and conjugated bilirubin, as the liver's conjugation process would still be operational.

**Option B:** Trapping of unconjugated bilirubin by a bile stone is not a mechanism for post-hepatic jaundice. Obstructive jaundice is characterized by a blockage in the bile ducts, which prevents conjugated bilirubin from being excreted.

**Option D:** Increased UDP-glucuronyltransferase activity would lead to an increase in conjugated bilirubin, but this is not the primary reason for the increased concentration of conjugated bilirubin in post-hepatic jaundice.

**Clinical Pearl / High-Yield Fact**
A key distinction between pre-hepatic and post-hepatic jaundice is the presence of conjugated bilirubin in the blood. In pre-hepatic jaundice, both unconjugated and conjugated bilirubin levels are elevated. In post-hepatic jaundice, unconjugated bilirubin levels remain relatively low, whereas conjugated bilirubin levels are elevated.

**✓ Correct Answer: C. The conjugation process of bilirubin in liver remains operative without any interference.**