THE THERMOMETRIC SUBSTANCE OF AN ABSOLUTE THERMOMETER IS

• A. alcohol
• B. mercury
• C. helium
• D. platinum ✓

The answer to the question is: D. platinum

An absolute thermometer is a type of thermometer that measures temperature based on an absolute scale, such as the Kelvin scale. The thermometric substance used in an absolute thermometer is typically a material that exhibits consistent and predictable changes in its physical properties with changes in temperature. The options provided are alcohol, mercury, helium, and platinum. Among these options, the most suitable thermometric substance for an absolute thermometer is platinum.

Platinum is often used as the thermometric substance in absolute thermometers due to its unique physical properties. It is a noble metal with a high melting point and excellent resistance to corrosion, making it highly stable and reliable for temperature measurement purposes. Additionally, platinum undergoes predictable changes in its electrical resistance with variations in temperature, which allows for accurate temperature measurements.

In the context of absolute thermometry, platinum resistance thermometers (PRTs) are commonly used. PRTs utilize the temperature-dependent resistance of platinum to measure temperature accurately. The relationship between the electrical resistance of platinum and temperature is well-characterized and can be used to establish a precise temperature scale.

Furthermore, platinum’s use as a thermometric substance in absolute thermometers aligns with the principles of the International Temperature Scale (ITS-90), which provides a standardized reference for temperature measurements. The ITS-90 relies on fixed points, such as the triple point of water, to define temperature scales, and platinum resistance thermometers play a crucial role in realizing and maintaining these scales.

In summary, among the options provided, platinum is the most suitable thermometric substance for an absolute thermometer due to its stability, reliability, and predictable temperature-dependent properties.