The Henry's law constant for oxygen gas in water at 25 °C is kh = 1.3×10⁻³ m/atm. At equilibrium, what is the partial pressure of O2 above a solution with an O2 concentration of 2.3×10⁻⁴ m (at 25 °C)?

A) 1.8 x 10⁻⁷ atm
B) 1.8 x 10⁻⁴ atm
C) 1.8 x 10⁻⁵ atm
D) 1.8 x 10⁻⁶ atm