What Is the [H₃O⁺] in a Buffer That Consists of 0.30

Multiple Choice

What is the [H₃O⁺] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa? [K_a(HCOOH) = 1.7 × 10^-4]

A) 1.1 × 10^{-4 M}
B) 2.6 × 10^{-4 M}
C) 4.3 × 10^{-4 M}
D) 6.7 × 10^{-5 M}
E) 1.7 × 10^{-4 M}