<u>Answer:</u> The mass of sample A after given time is 99.05 g.
<u>Explanation:</u>
All the radioactive reactions follows first order kinetics.
The equation used to calculate half life for first order kinetics:
We are given:
Putting values in above equation, we get:
Rate law expression for first order kinetics is given by the equation:
where,
k = rate constant =
t = time taken for decay process = 84.2 s
= initial amount of the reactant = 250 g
[A] = amount left after decay process = ?
Putting values in above equation, we get:
Hence, the mass of sample A after given time is 99.05 g.