Answer: 1.2 millimoles will be left after 2250 years
Step-by-step explanation:
Expression for rate law for first order kinetics is given by:
where,
k = rate constant
t = age of sample
a = let initial amount of the reactant
a - x = amount left after decay process
a) for completion of half life:
Half life is the amount of time taken by a radioactive material to decay to half of its original value.

b) Amount left after 2250 years
Thus 1.2 millimoles will be left after 2250 years