The First Order Gas-Phase Process: C₂H₆ → 2 CH₃ Has

The first order gas-phase process: C₂H₆ → 2 CH₃ has a rate constant, k = 5.36 × 10^-4 s^-1 at 700 °C. If in a reaction vessel, the initial concentration of ethane was 0.05 mol dm^-3, what is its concentration after 250 s?

A) - 0.084 mol dm^-3
B) 0.034 mol dm^-3
C) 0.044 mol dm^-3
D) -3.13 mol dm^-3