Classification — instruments and what they measure: identify the single incorrect pairing.

Introduction / Context:
This set checks factual knowledge of common instruments and their measured quantities. Three pairs are correct; one is wrong.

Given Data / Assumptions (corrected where needed):

• Ammeter → measures electric current.
• Speedometer → measures speed (updated from “Odometer : Speed”; odometer measures distance).
• Seismograph → records seismic waves/earthquake activity.
• Hygrometer → measures humidity, not pressure.

Concept / Approach:
Validate each mapping against standard definitions; the sole incorrect pair is the answer.

Step-by-Step Solution:

Verification / Alternative check:
Cross-compare: humidity↔hygrometer, pressure↔barometer, distance↔odometer, speed↔speedometer.

Why Other Options Are Wrong:
They are correct instrument→quantity matches.

Common Pitfalls:
Confusing odometer and speedometer; we have normalized to keep a single incorrect item.

Final Answer:
Hygrometer : Pressure