**Core Concept**
Acute Hepatitis B diagnosis relies on identifying serological markers indicative of an active infection. The correct marker should be present in the early stages of the disease, before the onset of immunity or chronic infection.

**Why the Correct Answer is Right**
IgM Anti-HBc is the correct answer because it is a marker of recent infection. IgM antibodies typically appear early in the course of an acute infection, often within the first few weeks. In the case of Hepatitis B, IgM Anti-HBc is produced in response to the core antigen (HBcAg) and is indicative of an active, acute infection. This marker is particularly useful in distinguishing between acute and chronic Hepatitis B infections.

**Why Each Wrong Option is Incorrect**
**Option A:** IgG Anti-HBc is a marker of past infection and immunity. It is not indicative of an acute infection and can be present in individuals who have recovered from Hepatitis B.

**Option B:** Anti-HBs is a marker of immunity, either from past infection or vaccination. It is not indicative of an acute infection.

**Option D:** HBsAg is a marker of active infection, but it does not distinguish between acute and chronic infections. It can be present in both acute and chronic Hepatitis B infections.

**Clinical Pearl / High-Yield Fact**
In cases of suspected Hepatitis B infection, the presence of IgM Anti-HBc in conjunction with HBsAg is highly suggestive of acute infection. This distinction is crucial for guiding treatment decisions and preventing the transmission of the virus.

**✓ Correct Answer: C. IgM Anti-HBc**