David kept 100 grams of radioactive sodium in a container. he observed the amount of sodium left in the container after regular intervals of time and recorded them in the table shown below.

time (hours) amount of sodium in container (in grams)
0 100
15 50
30 25
45 12.5

based on the observations, which of these is most likely david's inference?
a. the half life period of radioactive sodium is 15 hours.
b. the half life period of radioactive sodium is 50 hours.
c. the amount of sodium left in the container after 60 hours will be 10.5 grams.
d. the amount of sodium left in the container after 60 hours will be 1.5 grams.