Ammonia is produced from hydrogen and nitrogen, according to the equation: N₂(g) + 3H₂(g) ⇌ 2NH₃(g) The graph shows the yield of ammonia produced at 200°C and 100 kPa - HSC - SSCE Chemistry - Question 14 - 2002 - Paper 1

At higher temperatures, according to Le Chatelier's principle, the equilibrium shifts to favor the endothermic reaction. Since the synthesis of ammonia is exothermic, increasing the temperature should result in a lower yield of ammonia at equilibrium.

For the situation at 200°C, the graph shows a gradual increase in yield, suggesting that the reaction is approaching equilibrium. At 400°C, the yield should initially increase more sharply but will end at a lower eventual yield compared to the 200°C scenario due to the temperature favoring backward reaction.

Thus, the graph that correctly represents this behavior is graph C, where the yield at 400°C is depicted as lower than that at 200°C.