Fixed-point reference in thermometry: the internationally recognized silver point (melting point of pure silver at standard pressure) corresponds approximately to which temperature in °C?
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A760.5
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B860.5
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C960.5
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D1060.5
Answer
Correct Answer: 960.5
Explanation
Introduction / Context:In temperature metrology, metal fixed points (freezing/melting points of pure metals) provide precise calibration references. The silver point is one of the high-temperature fixed points used to calibrate radiation and contact thermometers.
Given Data / Assumptions:
- Pressure is at or near 1 atm (standard atmospheric pressure).
- Pure silver in thermal equilibrium at its melting/freezing plateau.
- Approximate tabulated values are acceptable for MCQ selection.
Concept / Approach:The silver point is commonly cited near 961 °C. For selection among rounded MCQ choices, 960.5 °C is the closest reasonable figure to the accepted value (about 961 °C), reflecting the temperature plateau observed during melting/freezing of pure silver.
Step-by-Step Solution:
Identify the fixed point of interest: silver (Ag) melting/freezing point.Recall approximate accepted value: ≈ 961 °C.Choose the closest option: 960.5 °C.Verification / Alternative check:Calibration tables for ITS-90 list the silver point very close to 961 °C; rounding differences explain the offered 960.5 °C choice.
Why Other Options Are Wrong:
760.5 °C and 860.5 °C: too low for silver; no standard metal fixed point at those temperatures for silver.1060.5 °C: closer to the melting point of gold (≈ 1064 °C), not silver.Common Pitfalls:Confusing the silver point (≈ 961 °C) with the gold point (≈ 1064 °C) or the antimony point (≈ 631 °C).
Final Answer:960.5