**Core Concept**
Obstructive jaundice occurs when there is a blockage in the bile ducts, leading to a buildup of bilirubin in the blood. This condition triggers an increase in certain enzymes to compensate for the obstruction.

**Why the Correct Answer is Right**
In obstructive jaundice, the enzyme alkaline phosphatase (ALP) is specifically increased due to its role in the transport of bilirubin and bile salts across cell membranes. ALP is produced by the bile ducts, liver, and other tissues, and its levels rise in response to bile duct obstruction. This increase in ALP helps to diagnose obstructive jaundice.

**Why Each Wrong Option is Incorrect**
**Option A:** Gamma-glutamyltransferase (GGT) is also elevated in obstructive jaundice, but it is not the specific enzyme increased in this condition.
**Option B:** Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are liver enzymes that rise in conditions of liver cell damage, such as hepatitis or cirrhosis, but not specifically in obstructive jaundice.
**Option D:** Lactate dehydrogenase (LDH) is a nonspecific enzyme that can be elevated in various conditions, including liver damage, but it is not the specific enzyme increased in obstructive jaundice.

**Clinical Pearl / High-Yield Fact**
Remember that alkaline phosphatase (ALP) is a key enzyme in diagnosing obstructive jaundice, and its levels can help differentiate it from other liver conditions. A high ALP level in combination with elevated bilirubin and other liver enzymes supports the diagnosis of obstructive jaundice.

**Correct Answer: C. Alkaline phosphatase**