The number of eutectics in the phase diagram of Fe₂Cl₃ - water system is -

CONCEPT:

Phase Diagram of Fe₂Cl₃ - Water System

• A phase diagram depicts the stable phases of a mixture as a function of temperature and composition.
• Eutectic Point:
  • The point at which a mixture of substances melts or solidifies at a single, fixed temperature, which is lower than the melting points of the individual components.
  • In a eutectic system, multiple eutectic points can exist depending on the complexity of the mixture.
• For the Fe₂Cl₃ (ferric chloride) - water system, the number of eutectic points indicates the different compositions where eutectic mixtures form.

EXPLANATION:

Ferric chloride forms four different stable crystalline hydrates (new compounds) having congruent melting points i.e., these are stable upto their melting points. The names of four hydrates of ferric chloride formed, their
composition and the corresponding melting points are summarised as under:

The formation of these compounds (hydrates) increases the number of areas
and eutectic points in the phase diagram. However, it does not introduce any
new feature. If we consider each newly formed compound as a new
component the significance of the different areas, lines, and points can be
easily understood. A schematic phase diagram of the ferric chloride-water
system.

The correct option for the number of eutectics in the phase diagram of Fe₂Cl₃ - water system is 5.