**Core Concept**
The functional unit of the liver responsible for metabolic and detoxification activities is the **liver acinus**, a region of hepatocytes arranged in a radial pattern around a central vein, enabling efficient blood flow and metabolic function.

**Why the Correct Answer is Right**
The **liver acinus** is the smallest functional unit of the liver, consisting of hepatocytes organized in a cone-shaped structure radiating from a central vein. It receives blood from both hepatic artery and portal vein, and its structure allows for efficient processing of nutrients, toxins, and drug metabolism. This unit operates independently and is the site of most metabolic reactions, making it the true functional unit.

**Why Each Wrong Option is Incorrect**
Option A: **Hepatocytes** are individual liver cells that perform functions like detoxification and protein synthesis, but they are not a "unit" in the anatomical sense—rather, they are the building blocks within larger structures.
Option B: **Portal tracts** are anatomical structures that connect the portal vein to the hepatic lobule, serving as conduits for blood and bile, not functional units.
Option D: **Hepatic lobule** is a larger anatomical structure containing multiple acini and is considered a structural unit, not the smallest functional one.

**Clinical Pearl / High-Yield Fact**
Remember: The **liver acinus** is the functional unit, while the **hepatic lobule** is a structural unit—this distinction is critical in understanding liver perfusion and disease patterns like cirrhosis or fatty liver.

✓ Correct Answer: C. Liver Acinus