Current Question: An isotope has a half-life of 34
mins. If you start with 26 g,
how many will remain after 238
mins?

26

0.1

0.2

25

0.2g

Explanation:

All radiodecay follows the 1st order decay equation

A = A₀e^-kt

A => Activity at time (t)

A₀ => Initial Activity at time = 0

k => decay constant for isotope

T => time in units that match the decay constant

Half-Life Equation => kt(½) = 0.693 => k = 0.693/34 min = 0.0204min¹

A = A₀e^-kt  = (26g)e^-(0.0204/min)(238min) = (26g)(0.0078) = 0.203g ~ 0.2g (1 sig fig).

a is the correct answer