The Rate Constant for a First Order Reaction Has the Value

The rate constant for a first order reaction has the value of 1.25×10^-3s^-1. If the initial concentration of reactant is 2.5 mol·L^-1, what will be the molar concentration of the reactant after 5 minutes?

A) 2.31
B) 1.72
C) 2.49
D) 0.78
E) none of the above