Which phrase describes velocity? a. a synonym for speed b. a vector quantity c. a quantity with magnitude only d. a quantity with no units

Velocity is a vector quantity.  Speed is a scalar quantity.  While the magnitude (number) of speed and velocity may be equal, what makes velocity a vector quantity is that it includes a direction.  Speed is a scalar quantity because there is no direction associated with it.

The correct answer is B: A vector quantity.

wavelength divides in half and speed stays the same.