What is the equilibrium constant expression, ${K_{\text{c}}}$, for the following reaction?

$${{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}{\text{(g)}} \rightleftharpoons {\text{2N}}{{\text{O}}_{\text{2}}}{\text{(g)}}$$

A.     ${K_{\text{c}}} = \frac{{[{\text{N}}{{\text{O}}_2}]}}{{[{{\text{N}}_2}{{\text{O}}_4}]}}$

B.    ${K_{\text{c}}} = \frac{{{{[{\text{N}}{{\text{O}}_2}]}^2}}}{{[{{\text{N}}_2}{{\text{O}}_4}]}}$

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

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

B