The initial concentration of a reactant in a first order reaction is 735 x 10" M. What will be its concentration after 4 half-lives? 1.84 x 10-3 M O b. 4.59 x 10-4 M O c. 9.87 x 10-4 M. O d. 9.19 x 10-4 M O e. 9.58 x 10-4 M O x