Figure $1$ shows the binary eutectic $Ag-Cu$ phase diagram and $g-x_{Cu}$ diagram at $850C.$

a$)$ Explain how the phase equilibria at $850C($observed from the phase diagram$)$ is based

on $($or derived from$)$ the Gibbs energy diagram. $(3$p$)$

b$)$ What can you say about the mutual interaction between $Ag$ and $Cu$ in Fcc phase? $(1$p$)$

c$)$ Explain shortly what is chemical potential ${}_i^{}($i$.$e partial molar Gibbs free energy of

component $i$ in phase $)$ and how ${}_{Ag}^{\text{L}\text{i}\text{q}}$ and ${}_{Cu}^{\text{L}\text{i}\text{q}}$ can be $($graphically$)$ defined from the $g-x_{Cu}$

diagram at $850C,$ when the nominal composition of the alloy is $40$ at$-\%Cu?(1$p$)$

Figure $1$ a$)$ Binary Ag$-$Cu phase diagram and b$)g-x_{Cu}$ diagram from $Ag-Cu$ system at

$850C$