_________ in a particular direction is velocity.

The correct answer is option 3. Speed.

Speed in a particular direction is velocity.

Speed: Speed is a scalar quantity, meaning it only has magnitude (how fast something is moving) but no direction.

Direction: When you specify the direction along with the speed, it becomes velocity. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

For example, if a car is traveling at 60 kilometers per hour (speed), that's just a measurement of how fast it's moving. But if you say the car is traveling 60 kilometers per hour towards the east (speed and direction), that's its velocity.