Which of the following is not a scalar quantity?

Velocity is classified as a vector quantity rather than a scalar quantity. This distinction is due to the fact that velocity not only considers the magnitude of an object's speed but also its direction of motion. For instance, an object moving at 50 km/h east has a different velocity than an object moving at the same speed but in the opposite direction.

In contrast, the other options listed—length, volume, and time—are all scalar quantities. Scalars are defined by just a magnitude without direction. Length measures the distance from one point to another, volume quantifies the three-dimensional space occupied by an object, and time is a measure of duration. These quantities do not have any associated direction, making them fundamentally different from velocity.