What is the equilibrium constant expression for the reaction below?

\({\text{2N}}{{\text{O}}_2}{\text{(g)}} \rightleftharpoons {{\text{N}}_2}{{\text{O}}_4}{\text{(g)}}\)

A.     \({K_{\text{c}}} = \frac{{{{[{\text{N}}{{\text{O}}_2}]}^2}}}{{[{{\text{N}}_2}{{\text{O}}_4}]}}\)

B.     \({K_{\text{c}}} = \frac{{[{{\text{N}}_2}{{\text{O}}_4}]}}{{[{\text{N}}{{\text{O}}_2}]}}\)

C.     \({K_{\text{c}}} = \frac{{[{{\text{N}}_2}{{\text{O}}_4}]}}{{2[{\text{N}}{{\text{O}}_2}]}}\)

D.     \({K_{\text{c}}} = \frac{{[{{\text{N}}_2}{{\text{O}}_4}]}}{{{{[{\text{N}}{{\text{O}}_2}]}^2}}}\)

D