The difference between speed and velocity is that a) speed is a vector and requires a direction. b) speed is a vector and requires a magnitude. c) velocity is a vector and requires a direction. d) velocity is a vector and requires a magnitude.

C) velocity is a vector and requires a direction.

Explanation:

In physics, there are two types of quantities:

- scalars: these are quantities that have only a magnitude

- vectors: there are quantities that have both magnitude and direction

As an example, speed is a scalar while velocity is a vector. Therefore, speed has only a magnitude, while velocity has both magnitude and direction: therefore, the difference between the two quantities is that velocity is a vector and requires a direction, as stated in option C.