Answer:
6.76*10^-4 , or 6.8*10^-4 if you consider sig figs
Explanation:
This is a bit of a confusing question, since it incorrectly states that the acid disassociation constant is simply [H+][F-].
Ka = [H+][F-]/[HF] , so plugging in the values, we get
[tex]K=\frac{[2.6*10^{-3}][2.6*10^{-3}]}{[0.01]}\\K=\frac{[2.6*10^{-3}]^2}{[0.01]}\\K=0.000676=6.76*10^{-4}[/tex]
If we were to use the equation in the question, Ka=[H+][F-], we would get the answer 6.76 * 10^-6 , which is not the Ka for HF