Answer:
Graph D.
Step-by-step explanation:
When a radioactive substance loses its radioactivity, reduction in its amount represents exponential sequence and the graph represents the exponential graph.
So graph number 1 is invalid which is representing a linear graph.
Now amount of the radioactive substance is 6 milligrams in month 1. So the point on graph should be (6, 1).
After 1 month it reduces to half 3 milligram in 2nd month and the point will be (3, 2). Â
Similarly after 3rd and 4th month points will be (1.5, 3) and (0.75, 4).
These points have been plotted in graph number D only.
Therefore Graph D is the answer.