Consider the reversible reaction, N2+3H2 = 2NH3 + Heat. The yield of NH3 will be maximum at:

Explanation

Exothermic reaction is a reaction in which heat is given out. For exothermic reaction, by increasing temperature reaction move backwards and value of Kc decreases and by decreasing temperature reaction moves forward and value of Kc increases.Reactions involving only gases and having unequal number of moles,by increasing pressure reaction move to that side where number of moles are less. Since the reaction is exothermic, low temp will favour the product's (NH3) side. High pressure favours the side with lower no of moles which in this case is the product's side. So lower temperature and higher pressure will ensure maximum lead of NH3