Question

Suppose 128 radioactive atoms have a half-life of 15 seconds. Approximately how many radioactive atoms will be left after 60 seconds

Answer 1

C. 8

Step-by-step explanation:

correct on gizmo; After one half-life (15 seconds), about 64 radioactive atoms will remain, half of the original 128. After a second half-life passes (30 seconds total), about 32 radioactive atoms will remain, half of 64. After a third half-life passes (45 seconds), about 16 radioactive atoms will remain. A time of 60 seconds represents four half-lives, so about 8 radioactive atoms will remain.

Answer 2

8 electrons

Step-by-step explanation:

Number of atoms = 128

Half life = 15 s

After each half life, the number of atoms reduces by half. So we need to determine how many half lives are in 60s.

Number of half lives = 60s / 15s = 4

After the first life;

Number of electrons left = 128 / 2 = 64

After the second life;

Number of electrons left = 64 / 2 = 32

After the third half life;

Number of electrons left = 32 / 2 = 16

After the fourth half life;

Number of electrons left = 16 / 2 = 8