A quantity which requires magnitude and direction to be specified is

1. Analyze the question The question asks which quantity needs both magnitude (size) and direction to be fully described. That is the definition of a vector quantity.

2. Explain the concept

• Scalar quantities have magnitude only. Examples: temperature, distance, mass, speed, time, energy.
• Vector quantities have magnitude and direction. Examples: displacement, velocity, acceleration, force, momentum.

3. Solution: check each option

• A. Temperature: e.g. 30 °C. No direction is needed, so it is a scalar.
• B. Distance: e.g. 5 km. This is the total path length, with no direction, so it is a scalar.
• C. Displacement: e.g. 5 km north. This is the change in position in a particular direction, so it is a vector.
• D. Mass: e.g. 10 kg. No direction is needed, so it is a scalar.

4. Answer Only displacement needs both magnitude and direction, so the correct option is C.

5. Exam tip Remember the pairs: distance → displacement, speed → velocity. The first of each pair is a scalar, and the second is a vector. If you can put "towards the north" or "to the left" after a quantity and it still makes sense, it is a vector.