**Core Concept**
Hepatitis B surface antigen (HBsAg) is the primary marker for acute hepatitis B infection. The body's immune response to HBsAg triggers the production of antibodies, which can be used to diagnose and monitor the disease.

**Why the Correct Answer is Right**
The first antibody to appear in the plasma/blood in acute hepatitis B is the antibody to hepatitis B surface antigen (anti-HBs), specifically IgM anti-HBs. This is because the immune system initially produces IgM antibodies in response to a new antigen. IgM anti-HBs is a marker of acute infection and is often used to differentiate between acute and chronic hepatitis B.

**Why Each Wrong Option is Incorrect**
**Option A:** IgG anti-HBs is incorrect because it typically appears later in the course of infection and is associated with immunity to hepatitis B.
**Option B:** IgM anti-HBc is incorrect because it is a marker of acute hepatitis B infection, but it is not the first antibody to appear in the plasma/blood.
**Option C:** IgG anti-HBc is incorrect because it is a marker of chronic hepatitis B infection and is not the first antibody to appear in the plasma/blood.

**Clinical Pearl / High-Yield Fact**
Remember that IgM anti-HBs is a sensitive marker for acute hepatitis B infection, but it can be negative in some cases, particularly in patients with severe liver dysfunction or those who are immunocompromised.

**Correct Answer: D. IgM anti-HBs**