**Core Concept**
High copper amalgam is a type of dental restorative material that contains a higher percentage of copper compared to traditional amalgam. The phase elimination in high copper amalgam is related to the changes in the microstructure of the material during the setting process.

**Why the Correct Answer is Right**
In high copper amalgam, the phase that is eliminated is Gamma 2. This is because the presence of copper in high concentrations alters the solubility and reactivity of the constituent phases, particularly the Gamma 2 phase. The Gamma 2 phase is a copper-rich phase that is present in traditional amalgam, but it is less stable in high copper amalgam. As a result, the Gamma 2 phase is eliminated during the setting process, leading to changes in the microstructure and properties of the material. The elimination of Gamma 2 phase is attributed to the reduced solubility of copper in the matrix phase, which allows it to precipitate out and form a more stable phase.

**Why Each Wrong Option is Incorrect**
**Option A:** Gamma 1 is not eliminated in high copper amalgam, as it is a more stable phase that is present in both traditional and high copper amalgam. The presence of copper does not affect the stability of the Gamma 1 phase.
**Option C:** While the presence of copper does alter the microstructure of the material, it is specifically the Gamma 2 phase that is eliminated, not both Gamma 1 and 2 phases.
**Option D:** The elimination of a phase is a characteristic of high copper amalgam, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
A key aspect of high copper amalgam is its improved corrosion resistance due to the elimination of the Gamma 2 phase. This makes it a suitable choice for dental restorations in areas with high corrosion potential, such as in the presence of saliva or acidic substances.

**✓ Correct Answer: B. Gamma 2**