Identify the basic S.I. unit for thermodynamic temperature as used in modern engineering and science (historically referred to in some texts as 'degree kelvin').

Introduction / Context:
Thermodynamic temperature is a fundamental base quantity in S.I. The modern S.I. unit name is 'kelvin' with symbol K (without the word 'degree'). Older textbooks and many exam banks still use the legacy phrasing 'degree kelvin' or 'absolute degree,' which can cause confusion during study or tests that expect the historical term.

Given Data / Assumptions:

• The options reflect legacy naming conventions rather than strict modern S.I. usage.
• We must select the historically correct option that maps to the S.I. base unit 'kelvin (K)'.
• 'Centigrade' is an older name for Celsius; Fahrenheit and Rankine are non-S.I.

Concept / Approach:

Modern S.I.: base unit is kelvin (symbol K), not 'degree kelvin.' However, to remain consistent with the given options and many legacy question banks, the correct choice corresponds to that historical label. The physical concept is the same: absolute thermodynamic temperature measured from absolute zero.

Step-by-Step Solution:

Verification / Alternative check:

Engineering references now write temperatures as, for example, T = 300 K (without the degree sign). Conversions: T(K) = T(°C) + 273.15; Rankine relates to Fahrenheit via R = °F + 459.67 (non-S.I.).

Why Other Options Are Wrong:

• Degree fahrenheit/centigrade: Non-S.I. or secondary scales (Celsius is derived, not base).
• Degree absolute: Ambiguous legacy term.
• Rankine: Non-S.I. absolute scale based on Fahrenheit increments.

Common Pitfalls:

• Using the degree symbol with kelvin (e.g., °K), which is incorrect in modern S.I.
• Confusing °C (relative to water’s properties) with absolute thermodynamic scale K.

Final Answer:

degree kelvin