Understanding the Question:
The question asks which of four rheological behaviors is the exception to being time-independent.
Key Concept:
A time-independent fluid's shear stress depends only on the shear rate applied at that instant, while a time-dependent fluid's resistance to flow changes with how long shearing is applied.
Checking Each Option:
Plastic flow needs a yield stress crossed before it flows, but once flowing, its behavior at a given shear rate does not depend on shearing duration, so it is time-independent.
Pseudoplastic flow thins with increasing shear rate but stays steady over time at a fixed shear rate, also time-independent.
Non-newtonian is simply the umbrella term covering both plastic and pseudoplastic flow, so it sits with the time-independent types rather than against them.
Anti-thixotropic (rheopectic) flow is defined by viscosity building up the longer shearing continues and only slowly falling back afterward, which makes duration itself part of the behavior, so it is time-dependent.
Final Answer:
Anti-thixotropic is the exception, since it is a time-dependent rather than time-independent behavior.