In materials of the same phase, or state of matter, the speed of sound tends to decrease as the density increases. Is this true or false and why?

False because the molecules of a denser substance have less inertia and move very quickly as compared to molecules of a less dense substance.

True because the molecules of a denser substance have less inertia and do not move as quickly as molecules of a less dense substance.

False because the molecules in all substances have no inertia so it does not have any effect.

True because the molecules of a denser substance have greater inertia and do not move as quickly as molecules of a less dense substance.

Ibelieve your answer is b.hope this : )

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero.