What Is the Hydronium Ion Concentration of a 0 $K _ { \mathrm { a } } = 3.5 \times 10 - 8 ?$

Multiple Choice

What is the hydronium ion concentration of a 0.150 mol L^-1 hypochlorous acid solution with $K _ { \mathrm { a } } = 3.5 \times 10 - 8 ?$ The equation for the dissociation of hypochlorous acid is below: $$\mathrm { HOCl } ( a q ) + \mathrm { H } _ { 2 } \mathrm { O } ( l ) \rightleftharpoons \mathrm { H } _ { 3 } \mathrm { O }^ + ( a q ) + \mathrm { OCl } ^ { - } ( a q )$$

A) 1.9 × 10^-4 mol L^-1
B) 7.2 × 10^-4 mol L^-1
C) 2.8 × 10^-5 mol L^-1
D) 7.2 × 10^-5 mol L^-1