What is the equilibrium constant expression, \({K_{\text{c}}}\), for the formation of hydrogen iodide from its elements?

\[{{\text{H}}_{\text{2}}}{\text{(g)}} + {{\text{I}}_{\text{2}}}{\text{(g)}} \rightleftharpoons {\text{2HI(g)}}\]

A.     \({K_{\text{c}}} = \frac{{{{{\text{[HI]}}}^2}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} \times {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

B.     \({K_{\text{c}}} = \frac{{{\text{[2HI]}}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} + {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

C.     \({K_{\text{c}}} = \frac{{2{{{\text{[HI]}}}^2}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} + {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

D.     \({K_{\text{c}}} = \frac{{{\text{[2HI]}}}}{{{\text{[}}{{\text{H}}_2}{\text{]}} \times {\text{[}}{{\text{I}}_2}{\text{]}}}}\)

A

\({K_{\text{c}}}\) expressions often leave much to be desired so it was encouraging to see that this was the easiest question on the paper with 93% of answers correct.