Consider process dynamics statements about transfer lag and system interaction. Identify the incorrect statement among the following descriptions of first-order and higher-order systems and interacting tanks.

Introduction / Context:
Control engineers distinguish between capacity (dynamic) lags and transfer (transportation or dead-time) lags. This question probes your understanding of transfer lag versus system order and the notion of interacting versus non-interacting processes, such as jacketed vessels where energy exchange couples dynamics.

Given Data / Assumptions:

• Single first-order system: one energy or material storage with no pure time delay.
• Higher-order systems: multiple storages in series or interacting.
• Transfer lag (dead time) refers to a pure time delay e^{-θs} component.

Concept / Approach:
A first-order system without transport effects exhibits capacity lag but not transfer lag. Higher order does not automatically imply transfer lag; dead time arises from transport phenomena (e.g., material flow in long pipes, sensing delays) or from approximations of many small lags in series. Interaction occurs when states influence each other, as in a jacketed stirred tank where process and jacket temperatures mutually affect dynamics.

Step-by-Step Solution:
Evaluate (a): A single first-order element has no pure dead time — statement is correct.Evaluate (b): Jacketed stirred tank is interacting due to coupled energy balances — statement is correct.Evaluate (c): Claiming all higher-order systems inherently have transfer lag is incorrect; higher order may still have zero dead time — this is the wrong statement.Evaluate (d): As the number of cascade stages decreases, the approximation to dead time weakens, hence apparent transfer lag decreases — statement is acceptable.

Verification / Alternative check:
Classical models show that N equal first-order lags in series approximate a dead-time element as N increases. Conversely, fewer stages reduce the approximation to dead time, supporting option (d).

Why Other Options Are Wrong:
(a) Correct: only capacity lag is present.(b) Correct: a canonical interacting example.(d) Correct trend for reduced stage count.

Common Pitfalls:

• Equating higher order with dead time; they are distinct features.
• Confusing interacting with coupled feedback; interaction is internal coupling of states.
• Overlooking that dead time is often a transport or measurement artifact.

Final Answer:
Transfer lag is a characteristic of all higher order systems (other than first order systems).