Why can zero-noise extrapolation fail?

Question: Which condition most directly threatens the reliability of zero-noise extrapolation? A) The circuit contains both one-qubit and two-qubit gates B) The observable is diagonal in the computational basis C) The measured expectation values do not follow the assumed extrapolation model across the scaled noise levels D) The backend supports dynamical decoupling Correct: C Explanation: ZNE estimates a zero-noise value by fitting measurements taken at different effective noise levels. If noise scaling is inaccurate or the chosen extrapolation model is wrong, the extrapolated value can be biased or unstable. Topic: advanced quantum computing / zero-noise extrapolation / error mitigation