**Core Concept**
In Hepatitis B infection, the body's immune response and viral replication lead to the production of various markers, some of which are indicative of acute or chronic infection. The presence of these markers helps in diagnosing and managing Hepatitis B infection.

**Why the Correct Answer is Right**
The correct answer is hepatitis B surface antigen (HBsAg). HBsAg is a protein on the surface of the hepatitis B virus (HBV) and is the first detectable marker of HBV infection. It appears 1-12 weeks before the onset of symptoms and persists for varying periods in individuals with chronic HBV infection. HBsAg is a reliable indicator of HBV replication and is used to diagnose acute and chronic HBV infection.

**Why Each Wrong Option is Incorrect**
**Option A:** HBeAg (Hepatitis B e-antigen) is a marker of viral replication, but its presence is not always present in chronic infection, especially in patients with HBeAg-negative chronic hepatitis B.

**Option B:** Anti-HBc (antibody to hepatitis B core antigen) is a marker of past or present infection but does not distinguish between acute and chronic infection.

**Option C:** Anti-HBs (antibody to hepatitis B surface antigen) indicates immunity to HBV, either from vaccination or past infection. Its presence is not indicative of chronic HBV infection.

**Clinical Pearl / High-Yield Fact**
HBsAg and HBeAg are useful markers in monitoring the response to antiviral therapy in patients with chronic HBV infection. The absence of HBsAg and HBeAg is a good prognostic sign, indicating a reduced risk of transmission and a lower risk of progression to liver cirrhosis or hepatocellular carcinoma.

**Correct Answer:** C. HBsAg