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GATE 2026 Chemical Engineering, Q25 · Process Control

The correct answers are A. Its transfer function has a positive zero.; C. The initial direction of the step response is opposite to the final steady state value..

Question

A process exhibits an inverse response to a step input. Which of the following statements is/are necessarily TRUE about the process?

  • A. Its transfer function has a positive zero.
  • B. Its transfer function has a negative zero.
  • C. The initial direction of the step response is opposite to the final steady state value.
  • D. The system is unstable due to a zero in the right half of the s-plane.

Official answer: A. Its transfer function has a positive zero.; C. The initial direction of the step response is opposite to the final steady state value.

Why

GATE 2026 official key: (A, C). Inverse response arises from a positive (right-half-plane) zero, which makes the step response initially move opposite to its eventual steady-state direction. A RHP zero alone doesn't make the system unstable (that requires a RHP pole), so (D) is false.

Explanation cross-checked for consistency. Final answer matches the official IIT answer key.

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