Find the unit that does not fit in the series: Kelvin, Celsius, Fahrenheit, Joule, Rankine

Correct — D.
Rule: four of the five measure temperature, one does not.

Kelvin, Celsius, Fahrenheit and Rankine are all temperature scales, each with its own zero and its own degree size.

Joule is the SI unit of energy — work and heat are measured in it — so it is the unit that does not fit → option (d).

Why the others are wrong

• (a)
  Kelvin — Kelvin is the SI base unit of thermodynamic temperature, with its zero at absolute zero. It belongs with the other temperature scales.
• (b)
  Rankine — Rankine is an absolute temperature scale whose degree is the size of a Fahrenheit degree. It is the least familiar name, not the odd category.
• (c)
  Fahrenheit — Fahrenheit is a temperature scale: water freezes at 32 °F and boils at 212 °F at standard pressure. It groups with Kelvin, Celsius and Rankine.

Odd-one-out items group words by what they measure. Here the shared quantity is temperature.

Kelvin and Rankine are absolute scales: their zero is absolute zero. Celsius and Fahrenheit put their zero above it. All four still measure the same quantity.

A joule measures energy. Heat is energy in transit, which is why the joule sits close to temperature in physics, but it is a different quantity.

Key facts

• Kelvin (K) is the SI base unit of thermodynamic temperature, and 0 K is absolute zero.
• The joule (J) is the SI unit of energy, work and heat.
• Rankine is an absolute scale with Fahrenheit-sized degrees.
• Water freezes at 0 °C, 32 °F and 273.15 K at standard pressure.

Common traps

• Picking Rankine because it is the unfamiliar name
• Treating the joule as a temperature unit because heat is measured in it

No directly related past PYQ was found.