Final answer:
The speedometer measures a vehicle's instantaneous speed, whereas the odometer measures the total distance traveled. (option B)
Step-by-step explanation:
The instrument used to measure the instantaneous speed of a vehicle is a Speedometer. This device provides real-time information about how fast the vehicle is moving at any given moment without accounting for the direction of travel. On the other hand, a car's odometer measures the total distance traveled rather than displacement. When calculating the total distance traveled by using an odometer reading and dividing it by the time of the trip, you are determining the average speed, not the magnitude of average velocity. The average speed and the magnitude of average velocity are the same when the direction of travel doesn't change and is in a straight line.
When it comes to measuring the instantaneous speed of a vehicle, the instrument to rely on is the speedometer. Therefore, option (B) Speedometer is the correct answer. It plays a crucial role in helping drivers maintain safe and legal speeds while driving, contributing to overall road safety.