Which of the following is a scalar quantity?

Step 1: Analyze the question We need to identify which option has magnitude only (a scalar) and no direction.

Step 2: Key concept

• Scalar quantity: has magnitude only (e.g. mass, speed, distance, energy, time, temperature).
• Vector quantity: has both magnitude and direction (e.g. force, velocity, displacement, momentum, acceleration).

Step 3: Check each option

• A. Tension: This is a force exerted by a string, rope or cable, and it acts along the string. Force is a vector, so tension is a vector.
• B. Weight: Weight is W = mg, the force of gravity on a body. It acts vertically downward, so it is a vector.
• C. Impulse: Impulse = force × time = change in momentum. Since force and momentum are vectors, impulse is a vector.
• D. Mass: Mass is the amount of matter in a body. It has magnitude only (e.g. 5 kg) and no direction, so it is a scalar.

Step 4: Answer The only scalar quantity is Mass, which is option D.

Exam tip: Mass and weight are often confused. Remember that mass is scalar (measured in kg) while weight is a vector (a force, measured in newtons, pointing toward the Earth's centre). Any quantity that is a force, or is derived from force (like impulse), is a vector.