Answer: 3.72 M
Explanation:
Expression for rate law for first order kinetics is given by:

where,
k = rate constant = 
t = age of sample = 15.0 minutes
a = let initial amount of the reactant = 10.0 M
a - x = amount left after decay process = ?




The concentration of
in a solution after 15.0 minutes have passed is 3.72 M
The process of an atom releasing energy when it moves to a lower energy state is called emission.
It deteriorates. Definitely more than when you started.