International temperature scale segment: The platinum resistance thermometer is used as the international reference standard between which fixed points/limits?

Introduction / Context:
International temperature scales designate specific instruments and fixed points for calibration over defined ranges. The platinum resistance thermometer (PRT) anchors a major portion of this scale due to its linearity and stability, bridging low to moderately high temperatures with high accuracy.

Given Data / Assumptions:

• Reference fixed points include the triple point of hydrogen (about 13.81 K) and the freezing point of antimony (about 903.9 K).
• Within this range, PRTs provide highly reproducible resistance–temperature relationships.
• Beyond the upper limit, radiation thermometry and other fixed points take over.

Concept / Approach:
Historical and modern international scales (e.g., ITS-90) specify PRT usage between cryogenic and high-temperature metal fixed points. The stated numeric range (13.81 K to 903.9 K) is a numeric expression of the named fixed points (triple point of hydrogen and freezing point of antimony), hence both statements (a) and (b) are equivalent and correct.

Step-by-Step Solution:

Verification / Alternative check:
Metrology references for ITS-90 and earlier scales show PRTs assigned across these limits with interpolating equations.

Why Other Options Are Wrong:

• (d) Denies established standards.
• (e) Restricts range to water’s standard points only, which is far too narrow.

Common Pitfalls:
Confusing the role of PRTs with thermocouples at higher temperatures or with gas thermometry at the lowest extremes.

Final Answer:
Both (a) and (b)