Answer:
A. Exothermic
Explanation:
Let's consider the following reaction at equilibrium.
2 NO₂(g) ⇄ N₂O₄(g)
reddish brown colorless
In order to assess the effect of temperature on the equilibrium, we need to consider Le chatelier's principle: If a system at equilibrium suffers a perturbation, it will shift its equilibrium position to counteract such perturbation.
Let's suppose the reaction is exothermic.
Since it coincides with the experimental results, we can conclude that the reaction is exothermic.