Final answer:
The S.I. unit of speed (velocity) is meters per second (m/s), which is choice 4) m/s from the provided options. Velocity includes both magnitude and direction, making it a vector quantity.
Step-by-step explanation:
The S.I. unit of speed (velocity) is meters per second (m/s). This is choice 4) m/s from the options provided. Velocity is defined as a vector, meaning it has both magnitude and direction. Instantaneous velocity, denoted by v, is the velocity at a specific instant in time, or the average velocity over an infinitesimally small time interval. Units of velocity can also include kilometers per hour (km/h) and miles per hour (mi/h), among others, but m/s remains the standard unit in the S.I. system. When you divide the distance covered by the time taken, you get the velocity in m/s. For example, if a person travels one meter for every second elapsed, their velocity would be 1 m/s.