**Core Concept**
Acute Hepatitis B can be earliest diagnosed by detecting specific antibodies and antigens indicative of a recent infection. The presence of IgM antibodies to the hepatitis B core antigen (anti-HBc) is a hallmark of acute infection, as it signifies a recent exposure to the virus.

**Why the Correct Answer is Right**
IgM anti-HBc antibodies are produced in response to the hepatitis B virus (HBV) core antigen, which is a protein that makes up the core of the viral particle. During acute infection, IgM anti-HBc antibodies are the first line of defense and are detectable in the blood within 1-2 weeks after exposure to the virus. These antibodies are indicative of an active, acute infection, and their presence is a key diagnostic criterion for Hepatitis B. The presence of IgM anti-HBc antibodies also helps to differentiate acute from chronic infection.

**Why Each Wrong Option is Incorrect**
**Option B:** Hbs Ag (Hepatitis B surface antigen) is a marker of active infection, but its presence alone does not distinguish between acute and chronic infection. Hbs Ag can be present in both acute and chronic infections, making it less specific for diagnosing acute Hepatitis B.

**Option C:** IgC anti HBc abs is a typographical error and likely refers to IgG anti-HBc antibodies, which are present in both acute and chronic infections. IgG anti-HBc antibodies are indicative of a past or ongoing infection, but their presence does not distinguish between acute and chronic infection.

**Option D:** Anti HBs Ag ab (antibody to hepatitis B surface antigen) is a marker of immunity, either from vaccination or past infection. The presence of anti-HBs antibodies indicates that the individual has either been vaccinated against Hepatitis B or has recovered from an infection.

**Clinical Pearl / High-Yield Fact**
In cases of suspected acute Hepatitis B, it's essential to perform a thorough laboratory evaluation, including serological tests for HBs Ag, anti-HBc (IgM and IgG), and anti-HBs. The presence of IgM anti-HBc antibodies is a critical diagnostic criterion for acute infection, and its absence or presence in combination with other markers can help differentiate between acute and chronic infection.

**✓ Correct Answer: A. IgM anti HBc ab**