Phase terminology – state after complete evaporation from the liquid The state of a substance whose evaporation from its liquid state is complete is commonly referred to as:

Introduction / Context:
Thermodynamics distinguishes between phases and special names used for specific substances. After a liquid has completely evaporated, the substance is in the gaseous phase; general terminology is important for clarity.

Given Data / Assumptions:

• No liquid remains; the state is entirely gaseous at the prevailing pressure and temperature.
• Terminology is generic (not restricted to water).
• Equilibrium state is assumed.

Concept / Approach:
For any substance, the gaseous state coexisting with or derived from the liquid near saturation is called vapour. For water specifically, the term steam is used; when perfectly dry at saturation it is called dry saturated steam. In generic multiple-choice contexts, “vapour” is the broad, substance-agnostic term.

Step-by-Step Solution:
Identify that the liquid has fully evaporated → the phase is gaseous.Choose the general term for post-evaporation state: vapour.Note: for water, “steam” is common; however, the question does not limit to water.

Verification / Alternative check:
Steam tables are specific to water; refrigerant tables label the gaseous phase as refrigerant vapour, underscoring the general applicability of the term “vapour.”

Why Other Options Are Wrong:

• Perfect gas: an idealization with specific equation-of-state assumptions; not a phase label.
• Air: a particular gas mixture, not a phase of a single substance.
• Steam: correct for water specifically but not general to all substances; the question is generic.
• Liquid–vapour mixture: implies partial, not complete, evaporation.

Common Pitfalls:
Using “steam” as a universal term; it properly refers only to water in engineering usage.

Final Answer:
vapour