Answer: The rate constant is
Explanation ;
Expression for rate law for first order kinetics is given by:
where,
k = rate constant = ?
t = age of sample = 4.26 min
a = initial amount of the reactant = 2.56 mg
a - x = amount left after decay process = 2.50 mg
Now put all the given values in above equation to calculate the rate constant ,we get
Thus rate constant is [tex]0.334s^{-1}