The [H⁺] in a 1.0 M solution of Na₂CO₃ is (for H₂CO₃, Ka₁ = 4.3 x 10⁻⁷; Ka₂ = 5.6 x 10⁻¹¹)
a) 7.5 x 10⁻⁶
b) 6.6 x 10⁻⁴
c) 1.3 x 10⁻²
d) 7.5 x 10⁻¹³
e) none of these