13 a copper-nickel alloy of composition 70 wt% ni-30 wt% cu is slowly heated from a temperature of 1300c (2370f). (a) at what temperature does the first liquid phase form? (b) what is the composition of this liquid phase? (c) at what temperature does complete melting of the alloy occur? (d) what is the composition of the last solid remaining prior to complete melting?

explained

Explanation:

in the attachment is the image of  Cu-Ni phase diagram and a vertical line constructed at a composition of 70 wt% Ni-30 wt% Cu

(a) Upon heating from 1300°C, the first liquid phase forms at the temperature at which this vertical line intersects the ?-(? + L) phase boundary--i.e., about 1345°C

(b) The composition of this liquid phase corresponds to the intersection with the (? + L)-L phase boundary, of a tie line constructed across the ? + L phase region at 1345°C--i.e., 59 wt% Ni;

(c) Complete melting of the alloy occurs at the intersection of this same vertical line at 70 wt% Ni with the (? + L)-L phase boundary--i.e., about 1380°C;

(d) The composition of the last solid remaining prior to complete melting corresponds to the intersection with ?-(? + L) phase boundary, of the tie line constructed across the ? + L phase region at 1380°C--i.e., about 79 wt% Ni.