Which of the following is a vector quantity?
a) 83 ounces of liquid
b) 10 m/s down
c) 15 seconds of travel
d) 55 km/hr in a truck

b) 10 m/s down

Explanation:

Let's start by explaining that a vector is one that has a numerical value along with its units (called a module) and a direction, while a scalar is only determined with a number and its corresponding units, without direction.  

Then, if we are given a quantity with only a numerical value along with its units we will have a scalar, and when we have a quantity with its numerical value along with its units and also the direction is given, we will have a vector.

So, according to this explanation, the only option that fullfils the conditions of a vector is b:

10 m/s down

Because we have a numerical value (10) with ist units (meters per second) and its direction (down).