Answer:
A. 0.78 g
Explanation:
The half-life of F-20 (11 s) is the time it takes for half of it to decay.
After one half-life, half (50 %) of the original amount will remain.
After a second half-life, half of that amount (25 %) will remain, and so on.
We can construct a table as follows:
No. of Fraction Mass
half-lives t/s Remaining Remaining/g
0 0 1 25
1 11 ½ 12.5
2 22 ¼ 6.2
3 33 ⅛ 3.1
4 44 ¹/₁₆ 1.6
5 55 ¹/₃₂ 0.78
6 66 ¹/₆₄ 0.39
We see that 0.78 g of F-20 remain after five half-lives (55 s).