The following are derived units EXCEPT

Analyze the question: We need the option that is NOT a derived unit. Every other option is a derived unit, so the odd one out must be a fundamental (base) unit.

Concept: The SI base units are the metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol) and candela (cd). Derived units are formed by combining base units through multiplication or division.

Checking each option:

• A. kg m⁻³ is the unit of density (mass ÷ volume). It combines kg and m, so it is derived.
• B. N (newton) is the unit of force, equal to kg m s⁻². It is derived.
• C. Ns is the unit of impulse or momentum, equal to kg m s⁻¹. It is derived.
• D. m³ is the unit of volume (length × length × length). It is derived, since it is built from the base unit m.
• E. kg is the base unit of mass. It is fundamental, not derived.

Answer: E (kg) is the only fundamental unit, so it is the exception.

Exam tip: Memorise the seven base units. If an option is just one of them, with no powers, products or quotients, it is not derived. Be careful with m³, because it is a power of a base unit, which still makes it derived.