Question

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.

Answer 1

First we have to understand what a half life is. A half life is a measure of time when the amount of a certain object is 50% of the original amount. Hence the answer for this is letter A. The initial amount is 100. fifty percent of 100 is 50 and that happens after 15 hours. Hence, 15 hours is the half life period. 

Answer 2

Answer: A. The half life period of radioactive sodium is 15 hours.

Explanation:

Half life is the time taken by a reactant to reduce to its original concentration. It is designated by the symbol $t_\frac{1}{2}$.

Given:

At 0 hours the amount of sodium in container is 100 grams

After 15 hours , the amount of sodium in container is 50 grams which is half of the original amount of 100 grams.

It will take 15 hours for half of a 100 g sample to decay to half of the amount i.e. 50 grams.