Vector quantities have both magnitude and direction

Steps:

• Recall that scalar quantities have only magnitude, while vectors have magnitude and direction.
• Evaluate each option: density is mass per unit volume (magnitude only).
• Mass is the amount of matter (magnitude only).
• Volume is the space occupied (magnitude only).
• Weight is the gravitational force on an object (magnitude and direction).

Why D is correct:

• Weight is a force, defined as $\vec{W} = m \vec{g}$, with both magnitude (strength) and direction (downward).

Why the others are wrong:

• A. Density is a scalar, calculated as mass divided by volume, with no direction.
• B. Mass is a scalar measure of matter, independent of direction.
• C. Volume is a scalar describing three-dimensional space, with magnitude only.

Final answer: D