What Is the Hydronium-Ion Concentration of a 0 $\times$ 10^-10)at 25°C?
A) 1

What is the hydronium-ion concentration of a 0.25 M solution of HCN (K_a = 4.9 $\times$ 10^-10) at 25°C?

A) 1.6 $\times$ 10^-4 M
B) 3.3 $\times$ 10^-6 M
C) 2.1 $\times$ 10^-6 M
D) 1.1 $\times$ 10^-5 M
E) 4.4 $\times$ 10^-5 M