ANS:B - a binary mixture.

In the context of ternary liquid systems plotted on equilateral triangular coordinates (commonly known as ternary phase diagrams), the sides of the triangle represent the following:

1. A pure component: Each corner of the equilateral triangle represents a pure component of the system. For example, in a ternary phase diagram for a system consisting of three components A, B, and C, the corners of the triangle would represent pure A, pure B, and pure C, respectively.
2. A binary mixture: The line connecting two corners of the equilateral triangle represents a binary mixture of the corresponding pure components. For instance, the line connecting the corners representing pure A and pure B would represent all possible binary mixtures of components A and B.
3. A ternary mixture: The interior of the equilateral triangle represents ternary mixtures containing varying proportions of all three components A, B, and C. Each point within the triangle corresponds to a specific composition of the ternary mixture, with the coordinates indicating the relative proportions of the three components.
4. Partially miscible ternary system: Ternary phase diagrams can also depict partially miscible systems, where certain regions within the triangle represent phases that are not completely miscible with each other. In such cases, the boundaries or regions of immiscibility are indicated within the triangle.