What is not achieved by liquid agitation in standard tank agitators? Identify the exception.

Introduction / Context:
Agitators perform several tasks: blending, heat transfer enhancement, gas–liquid contact, suspending solids, and emulsification. However, some tasks require specific conditions or chemistry; simply stirring is insufficient to overcome fundamental thermodynamics such as immiscibility without a dispersive mechanism or surfactants.

Given Data / Assumptions:

• Baffled tanks with standard impellers (e.g., Rushton, PBT).
• No chemical reaction that changes miscibility.
• "Blending" is taken to mean achieving a single homogeneous phase.

Concept / Approach:
Agitation can disperse gas into a liquid (forming bubbles) and suspend solids by turbulent eddies. It can also disperse one immiscible liquid into another as droplets, creating an emulsion when aided by interfacial tension modifiers (surfactants). But "blending" immiscible liquids into a single, truly homogeneous phase is not accomplished by agitation alone; thermodynamic immiscibility persists, and once shear stops, the phases separate.

Step-by-Step Solution:
List typical accomplishments: gas dispersion, solids suspension, and emulsification.Identify the exception: creating a single-phase mixture from immiscible liquids is not possible by agitation.Therefore, choose "Blending of immiscible liquids."

Verification / Alternative check:
Process design texts distinguish between blending (miscible) and emulsification (immiscible). For immiscible systems, coalescence and separation occur without stabilizers or continuous shear.

Why Other Options Are Wrong:
Gas dispersion, emulsification, and solids suspension are canonical roles of agitators when operated at appropriate speeds and with suitable impellers.

Common Pitfalls:
Equating "well mixed" with thermodynamic homogeneity; immiscible systems remain two-phase despite good mixing.

Final Answer:
Blending of immiscible liquids.