Solution:

Phase : A phase is defined as a homogeneous part of a system that has uniform physical and chemical properties. Pure metal is considered to be a phase.

Phase diagrams are the diagrams which indicate the phase existing in the system at any temperature and composition. Y- axis of phase diagram indicates temperature and X-axis indicates weight percent of second element as abscissa. These diagrams are used to find out the amount of phases existing in a given alloy with their composition at any temperature. It also helps in understanding the phenomenon that occur during rapid heating and cooling of the alloy.