A Gas-Phase Decomposition Is First-Order with Respect to the Reactant

A gas-phase decomposition is first-order with respect to the reactant, R. If the initial concentration of R is 1.0 × 10⁻⁴ mol L⁻¹and the rate constant k = 1.08 × 10⁻⁶ s⁻¹, what concentration of R remains after 25 days?

A) 1.0 × 10 ⁻³ mol L ⁻¹
B) 1.0 × 10 ⁻⁴ mol L ⁻¹
C) 9.6 × 10 ⁻⁵ mol L ⁻¹
D) 4.3 × 10 ⁻⁵ mol L ⁻¹
E) 9.7 × 10 ⁻⁶ mol L ⁻¹