Which of the following temperature scales is the SI absolute temperature scale that starts at absolute zero?

Introduction / Context:
Temperature can be measured in several scales, including Celsius, Fahrenheit, Kelvin, and Rankine. In physics and engineering, absolute temperature scales that start at absolute zero are particularly important because many gas laws and thermodynamic relationships are simplest in these units. This question asks you to identify the SI absolute temperature scale that begins at absolute zero.

Given Data / Assumptions:

• Absolute zero is the theoretical temperature at which the thermal motion of particles is minimal.
• Celsius and Fahrenheit are relative scales with arbitrary zero points based on water properties.
• Kelvin and Rankine are absolute scales starting at absolute zero, but differ in step size.
• The SI system adopts one of these as its official base unit for temperature.

Concept / Approach:
The Kelvin scale is the SI base unit of thermodynamic temperature. It starts at absolute zero, which corresponds to 0 kelvin, and uses the same size degree as the Celsius scale. Rankine is an absolute temperature scale used mainly in some engineering contexts that also starts at absolute zero but uses the Fahrenheit degree size. Celsius and Fahrenheit have zero at the freezing point of water and at a chosen scale point, respectively, so they are not absolute. Since the question explicitly asks for the SI absolute scale, the Kelvin scale is the correct answer.

Step-by-Step Solution:
Step 1: Recall that absolute zero is defined as 0 K in the Kelvin scale. Step 2: Understand that the Kelvin scale is built so that 0 K corresponds to minus 273.15 degree Celsius approximately. Step 3: Recognise that the Celsius scale uses 0 degree at the freezing point of water and 100 degree at the boiling point at standard pressure, so it is not an absolute scale. Step 4: Note that the Fahrenheit scale uses 32 degree for the freezing point of water and 212 degree for boiling, also not absolute. Step 5: Rankine is absolute but is not the SI base unit, so when the question emphasises SI absolute scale, Kelvin is the required choice.

Verification / Alternative check:
Thermodynamics equations such as the ideal gas law PV = n R T require temperature in an absolute scale, usually Kelvin, in standard physics courses. Scientific literature and data tables always report fundamental thermodynamic properties in kelvin. The official SI brochure lists kelvin as one of the seven base units, confirming its status as the SI absolute temperature scale.

Why Other Options Are Wrong:
Rankine scale: It is an absolute scale, but based on Fahrenheit and is not the SI base unit for temperature. Celsius scale: It is a relative scale with zero at the freezing point of water and does not start at absolute zero. Fahrenheit scale: It is also a relative scale and not used as an absolute thermodynamic scale.

Common Pitfalls:
Students may know that both Kelvin and Rankine start at absolute zero and become unsure which one to choose. The key hint is the word SI in the question, pointing to Kelvin. Another confusion is mixing up degree symbols; Kelvin is now written simply as K without the word degree, reflecting its status as an absolute thermodynamic scale.

Final Answer:
The SI absolute temperature scale that starts at absolute zero is the Kelvin scale.