Object A moves with a constant velocity of - 10 m/s and object B moves with a constant velocity of 5 m/s. Which object has the larger speed?

Object A has the larger speed because speed is not a vector quantity, it is scalar. This means that directionality, or in this case the sign of the velocity, doesn't matter.

Speed = |velocity|

Object a speed = |-10|=10 m/s

Object b speed = |5|=5 m/s

Object a is the answer.