When a sample of $NO_2$ is placed in a container,this equilibrium is rapidly established: $2NO_{2(g)} \rightleftharpoons N_2O_{4(g)}$. If this equilibrium mixture is a darker colour at high temperatures and at low pressure,which of these statements about the reaction is true?

• A
  The reaction is exothermic and $NO_2$ is darker in colour than $N_2O_4$
• B
  The reaction is exothermic and $N_2O_4$ is darker in colour than $NO_2$
• C
  The reaction is endothermic and $NO_2$ is darker in colour than $N_2O_4$
• D
  The reaction is endothermic and $N_2O_4$ is darker in colour than $NO_2$