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.