Consider the reaction:
{HC}₂{H}₃{O}₂ ({aq}) leftharpoons {H}₂{O}({l}) + {H}₃{O}+({aq}) + {C}₂{H}₃{O}₂-({aq})
with K_c = 1.8 × 10⁻⁵ at 25°C. If a solution initially contains 0.205 M {HC}₂{H}₃{O}₂, what is the equilibrium concentration of {H}₃{O}+ at 25°C?
a) 1.8 × 10⁻⁵ M
b) 0.205 M
c) 1.025 × 10⁻⁵ M
d) 0.0001025 M