In a high copper amalgam, the phase which is eliminated is:: (A) Gamma 1, (B) Gamma 2, (C) Gamma 1 and 2, (D) No phase is eliminated
Answer is B. A reaction between Cu3 Sn (ε phase) and γ2 occurs and yields Cu6Sn5  (η phase). Because of the low copper content, a majority of γ2 remains. The addition of more than 6% of copper by weight can reduce or eliminate the γ2 phase by the formation of Cu-Sn phase.
Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 344