In a binary phase diagram, what does a eutectic point represent?

• A. The highest melting point of any mixture.
• B. The point where the liquid phase first disappears.
• C. The lowest melting temperature at which a mixture of the two components can melt into a liquid.
• D. A composition where only one solid phase exists at all temperatures.

Answer: (C)

In a binary phase diagram, the eutectic point is the composition and temperature where melting occurs at the lowest possible temperature for any mixture of the two components. At this specific point, the liquid can form and, upon cooling, the liquid solidifies into two solid phases simultaneously. This gives a sharp, single melting temperature—the same way a pure substance melts at a single temperature. So, the eutectic point represents the lowest melting temperature at which a mixture of the two components can melt into a liquid.