Answer :
If a substance has a half-life of 39.1 min, and there are initially 20.0 g of the substance 2.39 g will remain after precisely two hours.
N(t) = N0 (1/2)^t/t1/2
Nt = 20 (1/2)^120/39.1
Nt = 2.39 g
What is half life?
The time it takes for one-half of a radioactive isotope to decay is known as its half-life, and it is both an intriguing and practical feature of radioactive decay. An individual radioactive isotope's half-life is unaffected by environmental factors and is independent of the isotope's starting concentration.
N(t) = N0 (1/2)^t/t1/2
To learn more about half life click the given link
https://brainly.com/question/2320811
#SPJ4
