The Following Questions Refer to the Gas-Phase Decomposition of Chloroethane:C₂H₅Cl

The following questions refer to the gas-phase decomposition of chloroethane:C₂H₅Cl → products
Experiment shows that the decomposition is first order. The following data show kinetics information for this reaction.
-What was the initial concentration of the ethylene chloride?

A) 0.02 M
B) 0.22 M
C) 0.35 M
D) 0.29 M
E) 0.11 M