Which statement is completely accurate?

Atoms of the same element always have different atomic weights.
Atoms of the same element can have different numbers of neutrons.
Atoms of the same element always have different numbers of neutrons.
Atoms of the same element can have neutrons but exist without protons. c

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. 

Answer (d) the universe had cooled enough for atoms to combine, protons and neutrons were too far apart to form nuclei;