Answer:
(A) The value of Kc for this reaction increases as temperature increases, because the reaction is endothermic.
Step-by-step explanation:
N₂O₄ ⇌ 2NO₂
colourless reddish-brown
NO₂ is a reddish-brown gas, while N₂O₄ is colourless.
When you cooled the sample to 0 °C, the position of equilibrium shifted to form more N₂O₄, that is, it shifted to the left.
According to Le Châtelier's Principle, when a stress is applied to a system at equilibrium, the system will respond in a way that tends to relieve the stress.
You applied a stress: you removed heat from the system. It responded by shifting in the direction that produces more heat (to the left).
If you consider heat as part of the reaction, the equation must be
N₂O₄ + heat ⇌ 2NO₂
The reaction is endothermic.
Furthermore, since the position of equilibrium shifted in the direction of reactants, the equilibrium constant decreased.
The value of K decreases as the temperature decreases. If we say it the other way, the value of K increases as the temperature increases.
The correct answer is (A) The value of Kc for this reaction increases as temperature increases, because the reaction is endothermic.
(B) and (D) are wrong, because the reaction is endothermic.
(C) is wrong, because the value of Kc decreases as temperature decreases.