Answer
Please see the work below.
Work Step by Step
The chemical equation is
$HCN+H_2O\rightarrow \leftarrow H_3O^{+}+CN^{-}$
The equilibrium constant is given as
$K_a=\frac{[H_3O^+][CN^-]}{[HCN]}$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.