2 What does how much, how
long and how
often have to do with exposure to chemicals?

Well how much, how long, and how often  

For example how much is like how much a object is left in a small room with chemicals

How long is the time

how often is how much the same cycle is done repeatedly

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.