Among the listed thermocouples, identify the pair capable of measuring the highest temperatures (extreme high-temperature applications under protective atmospheres).

Introduction / Context:
Thermocouple upper limits depend on metallurgy and service environment. Noble-metal thermocouples operate reliably in oxidizing hot zones; refractory-metal combinations extend to even higher temperatures but require inert or vacuum atmospheres to avoid oxidation.

Given Data / Assumptions:

• Comparison is for maximum attainable temperatures, not routine stability in air.
• Protective atmosphere or vacuum is available for refractory pairs.
• Standard industrial pairings are implied.

Concept / Approach:
Chromel–alumel (Type K) and iron–constantan (Type J) serve low-to-mid ranges. Platinum–rhodium (Types S/R/B) reach ~1600–1700°C in oxidizing conditions. Tungsten-based refractory-metal pairs (e.g., W–Re or W–Mo) can measure up to ~2300–2600°C under vacuum or inert gas, which surpasses the noble-metal limits. Thus, for absolute maximum temperature capability, tungsten–molybdenum class leads.

Step-by-Step Solution:

Verification / Alternative check:
High-temperature furnace instrumentation commonly uses W-based thermocouples for temperatures above noble-metal capabilities when oxygen is excluded.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming “best in air” equals “highest temperature overall.” Refractory pairs demand special atmospheres.

Final Answer:
Tungsten–molybdenum (refractory metal)