Which of the following is a scalar quantity?

Speed is classified as a scalar quantity because it is defined solely by its magnitude and does not involve direction. Scalar quantities can be described by a single numerical value with units, such as miles per hour or meters per second, indicating how fast an object is moving without specifying the direction of that movement.

In contrast, velocity is a vector quantity, which means it has both magnitude and direction—indicating not just how fast an object is traveling, but also in which direction it is traveling. Similarly, force is also a vector quantity, as it describes an influence that causes an object to accelerate, requiring both magnitude (how strong the force is) and direction (where the force is applied). Acceleration, like force and velocity, is another vector quantity that specifies how quickly the velocity of an object changes, encompassing both the rate of change and the direction of that change.

Therefore, among the given options, speed stands out as the only scalar quantity, focusing solely on the rate of motion rather than the direction in which it occurs.